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Full text of "The chemistry of paints and painting"

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THE 

CHEMISTRY OF PAINTS AND PAINTING 



THE 

CHEMISTRY 



OF 



PAINTS AND PAINTING 



BY 

SIR ARTHUR H. CHURCH, K.C.V.O., F.R.S. 

M.A., D.Sc, F.S.A. 
Sometime Professor of Chemistry in the Royal Academy 0} Arts in London 



FOURTH EDITION 

REVISED AND ENLARGED 



LONDON 

SEELEY, SERVICE ^ CO. LIMITED 

38 Great Russell Street 

1915 



1500 



[Dedication oj the First and Second Editions.'] 



TO 

SIR FREDERIC LEIGHTON, BART., P.R.A,, 

WHO HAS ALWAYS SHOWN A DEEP INTEREST 

IN ITS SUBJECT, AND HAS GREATLY 

ENCOURAGED ITS AUTHOR, 

THIS BOOK 

IS, BY PERMISSION, DEDICATED. 



s\^ 




r-v^ . ft 



PREFACE 



This handbook first appeared in the spring of i8go ; two 
years afterwards a second and revised edition was pub. 
lished. In igoi, when the work had been for some time 
out of print, a thorough revision of its contents was 
carried out, a good deal of new matter being introduced, 
while a few pages, which had been occupied by a digest 
of an important newspaper discussion on the effect of 
light upon water-colour drawings, were not reprinted. 
This account was omitted because it could no longer be 
contended that many English water-colour drawings, ex- 
posed to strong light for a considerable length of time, 
had suffered no change in hue and depth. 

Various additions and corrections have been made in 
this, the fourth edition. A few of the paragraphs relating 
to rather recondite subjects have been abridged or even 
omitted. Indeed, an attempt has been made, in carrying 
out the present revision, to simplify, so far as possible, 
the way in which the results, obtained by chemists in the 
study of painters' materials, are presented to the artist 
and the student of art. 

In the year 1908 a German translation of the third 
edition of this book was published in Munich. It was 



viii PREFACE 

prepared and edited by the distinguished scientist Dr. 
Wilhelm Ostwald. I have incorporated with the present 
issue the substance of the paragraphs which he introduced 
into my original text ; these are indicated by the sign 1[. 

In preparing the following pages for the press, I have 
to acknowledge, as on previous occasions, the help of 
several friends and correspondents. Amongst these I 
specially name Mr. J. Scott Taylor, many of whose 
suggestions have been incorporated in the text, and also 
Dr. A. P. Laurie, my successor in the chair of Chemistry 
in the Royal Academy of Arts. 

Of recent years the literature dealing with the subjects 
to which the present handbook is devoted has greatly 
increased. Several of the volumes named in my 
* Bibliographical Notes ' are of sterling merit and contain 
original material of no little importance. But I am 
bound to confess that I have met with several disappoint- 
ments when searching for records of new facts in recent 
dictionary articles, reports of lectures, and treatises. On 
perusal a familiar note seemed sometimes to be struck ; 
and I ultimately identified not a little of the material as 
my own. I will not dwell on this matter ; it is indeed 
some consolation to feel that such transferences from my 
pages would not have taken place had not the paragraphs 
and tables and comments been deemed of some value. 
But I trust that I myself shall not be thought guilty of 
plagiarism because in 19 14 I reprint something, say a 
table or a classification, which I published in 1890, but 
which appeared ten years or more later as having been 



PREFACE ix 

devised by another chemist. Another reason for limiting 
the number of books included in my list of titles is to be 
found in the extensive Bibliography appended to Pro- 
fessor Laurie's ' The Materials of the Painter's Craft.' 

No very great differences will be found between the 
present and the preceding edition, but I have endeavoured, 
not only to introduce new matter which I think of import- 
ance, but to simplify and make more exact the treatment 
of the various subjects discussed ; and, in fine, to carry out 
more fully the plan set forth in the Preface (here re- 
printed) to the First Edition. 

Arthur H. Church. 

Kew Gardens, 

jfune 2, 1914. 



PREFACE TO THE FIRST EDITION 



In the present volume the materials and methods of the 
painter of pictures are viewed mainly from the chemical 
standpoint. An attempt has been made to treat in orderly 
sequence the various kinds of painting-grounds, the con- 
stituents of vehicles and varnishes, the pigments them- 
selves, and the chief processes of painting. Although 
the artistic side of the numerous problems discussed has 
not been neglected, the book is in no way intended to 
teach manipulation to art students. It has been written 
^^dth the view of explaining to artists, whether they be 
accomplished masters or commencing students, the chief 
chemical and physical characters of the materials with 
which they deal and of the operations they practise. In 
many instances a sketch of the processes for preparing 
certain pigments and varnishes is given, not in order to 
turn the painter into a colour-maker or a varnish-manu- 
facturer, but rather that he may acquire a clearer insight 
into the nature and properties of the most important con- 
stituents entering into the composition of his pictures. 
With regard, however, to the tests for purity and 
genuineness which I have described in the following pages, 



xii PREFACE TO THE FIRST EDITION 

my object in introducing them has been different, for I trust 
that (in some cases, at least) the easy experiments I have 
recorded will be tried, especially with suspicious pigments. 
The operations require but little time; the pieces of ap- 
paratus needed, like the chemicals, are few and inexpen- 
sive. And when the ease with which these testings can be 
made has been proved by practice, the experimenter may 
perhaps be induced to proceed a little farther, preparing his 
own siccative oil, selecting and purifying his spirit of tur- 
pentine, and so forth. That the painter should test the 
varnishes he buys for hardness and toughness, and the pig- 
ments for durability, may, I hope, be taken for granted. 

' Titian managed pretty well without chemistry, did he 
not ?' A distinguished artist asked me this question the 
other day. But not only were the conditions under which 
the painters of Titian's time worked simpler than those of 
the nineteenth century, but grounds, paints, oils, and var- 
nishes were generally prepared in the studios of the artists, 
and under their own superintendence, so that the chances 
of going wrong were comparatively limited. Audit is not 
to be denied that a better acquaintance with the nature of 
the materials which many of the old masters employed 
would have caused their works to be handed down in 
sounder preservation to future generations. 

It is possible — I hope, indeed, it is probable — that this 
book may be found of service to students who are purpos- 
ing to devote themselves to certain manufacturing and 
technical pursuits. I am aware that to those who refer to 



PREFACE TO THE FIRST EDITION xiii 

its pages for the revelation of all the secrets of colour- 
manufacturers it may prove in some measure disappoint- 
ing ; yet I trust that, in the way of information and 
suggestion, the study of this volume will not be unattended 
with advantage. It must be remembered that it is con- 
fessedly an elementary manual only, written with a defi- 
nite aim, but covering a very wide area of inquiry. And if 
chemists should conclude that it contains too little chem- 
istry, artists may perhaps think that it contains too much. 
There are repetitions in the following pages, for the 
topics discussed in some of the chapters overlap one 
another. I am perfectly aware of having made the same 
statement, given the same figure, and expressed the same 
opinion in more than one place. The scheme of the work 
required such repetitions. I felt sure that many an artist 
or student would turn to one section or other of the book 
without caring to read the whole. One inquirer would 
like to ascertain at once what pigments were safe, what 
dubious, what fugitive, by a reference to the tables in 
Chapters XXI. and XXII. ; while another, anxious to learn 
something of the evidence on which the several verdicts of 
approval or condemnation were based, would expect to 
find his requirements met in the pages devoted to trials of 
pigments. Again, under the names of the individual pig- 
ments, discussed in Chapters XIII. to XIX., some of the 
changes described in the last part of the work are quoted. 
Thus it happens that there are some materials common to 
all of those sections of the book just named. 



xiv PREFACE TO THE FIRST EDITION 

Much of the substance of the lectures which I have 
delivered before the Royal Academy since the year 1880 
has been incorporated with the present manual, but it is 
necessary to state that some of the original material to be 
found in the following pages has been long before the 
artistic world, and has found its way into the books and 
essays of other writers. I say this, not for the purpose of 
making reclamations of priority, but in order to prevent 
myself from being charged with plagiarism. For instance, 
so long ago as 1859, I described, for the first time, some of 
the artistic uses of solid paraffin in a paper on the pro- 
cesses of painting, read before the Oxford Architectural 
Society; further details were given in a lecture to the 
Architectural Association in 1862. On many other matters 
connected with the chemistry of paints and painting, new 
investigations and studies were published by me between 
the years 1867 3-^^ 1872, particularly in notes and essays 
entitled ' Chemical Aids to Art,' and ' The Chemistry of 
the Fine Arts.' But my statements and results, whether 
contained in the above publications or in my Academy 
lectures, have not been, in all instances, referred to their 
source, or reproduced with accuracy, while some have 
been overlooked or forgotten. 

In preparing the present volume I have made consider- 
able use of several of the works named in my Biblio- 
graphical Notes; I have consulted also the standard 
chemical dictionaries of Watts and of Wurtz, the treatise 
by Roscoe and Schorlemmer, besides many special papers 



PREFACE TO THE FIRST EDITION xv 

by other chemists. I wish I could have given an au- 
thority for every statement not derived from my personal 
experience, but in an elementary manual treating of 
many diverse topics such a plan, even if it could have 
been carried out, would have embarrassed my story with 
a multitude of perplexing references. 

I do not know of any one text- book which covers the 
same ground as the volume now offered to the public. 
Several small books on pigments — the most important of 
all the materials employed by the artist — have indeed been 
lately published, but the chemical information they afford 
is generally meagre, and sometimes far from exact. One 
recent little brochure, which lies before me, has, I confess, 
caused me some amusement not wholly unshaded with 
regret. The writer does not pose as a humourist, yet he 
tells us, when we test for lead in cadmium red, first to 
mix the sample with white lead before applying the usual 
test for that metal. Chinese vermilion, he informs us, is 
sulphide of arsenic, though it is really sulphide of mercury. 
The presence of sulphides of baryta and lime is stated in 
one place to lend a softness to the chromates of lead ; as 
these sulphides instantly blacken these brilliant chromates, 
perhaps they may be said to soften them. Coeruleum, a 
stannate of cobalt, is directed to be made of carbonate of 
soda, powdered flint, and oxide of copper, its two essential 
constituents, the oxides of tin and cobalt, not being named. 
These and many other equally preposterous statements 
and directions may afford merriment to the chemist, but 



xvi PREFACE TO THE FIRST EDITION 

it is indeed pitiable that such teaching should be seriously 
offered to artists and art-students. 

It is satisfactory to know that several accomplished 
chemists are now devoting themselves to the practical 
study and improvement of pigments. Mr. A. P. Laurie, 
Mr. H. Seward, and Mr. J. Scott Taylor, are all doing 
good work in this direction. 

It remains for me to express the hope that the readers 
of this volume will favour me with any material at their 
disposal which may serve for the correction and improve- 
ment of its pages. I am aware of having omitted to 
notice many interesting matters ; amongst these I include 
certain pigments, derived from coal-tar products, which 
have not yet been sufficiently tested. Then, too, the 
materials and methods of ceramic and glass painting have 
been excluded from consideration, mainly because their 
adequate treatment, while demanding much space, would 
have appealed to a comparatively limited group of 
students. 

If painters and chemists will grant me their help, I 

trust that I may further justify ;, by means of an improved 

edition of my book, the favourable reception which I hope 

may be accorded to the first. 

A. H. Church. 

Kew, March, 1890. 



BIBLIOGRAPHICAL NOTES 



Blockx, J., ' Peinture a I'Huile.' Pp. iv, 98. Gand, 

1881. 
Cennini, Cennino, 'The Book of the Art.' Translated 

into EngHsh by Mrs. C. J. Herringham, with 

Notes on Mediaeval Methods by the Translator. 

Pp. xxxviii, 288. London, 1899. 
Church-Ostwald, ' Farben und Malerei.' Pp. xii, 376. 

Miinchen, 1908. 
Eastlake, Sir C. L., 'Materials for a History of Oil- 

Painting.' Series I., pp. xii, 561 ; Series II., pp. xv, 

432. London, 1847, 1869. 
Field, G., ' Chromatography,' modernized by J. Scott 

Taylor. Pp. viii, 207. Second edition. London, 

1885. 
Hurst, G. H., ' Painters' Colours, Oils, and Varnishes.' 

Fifth edition, revised by Noel Heaton. Pp. xii, 528. 

London, 191 3. 
Jametel, Maurice, ' L'Encre de Chine.' Pp. xxx, 94. 

Paris, 1882. 
Lapparent, P. de, * Les Alterations des Couleurs.' 

Pp. 36. Paris [1900]. 
Laurie, A. P., * The Materials of the Painter's Craft in 

Europe and Egypt.' Pp. xvi, 444. London and 

Edinburgh, 1910. 



xviii BIBLIOGRAPHICAL NOTES 

Laurie, A. P., ' The Pigments and Mediums of the Old 

Masters.' Pp. xvi, 192. London, 19 14. 
Moreau-Vauthier, Ch., < La Peinture.' Pp. xii, 322. 

Paris, 191 2. 
Ostwald, W., ' Letters to a Painter.' Translated from 

the German by H. W. Morse. Pp. viii, 162. 

Boston, U.S.A., 1906. 
Parry, Ernest J., and Coste, John H., *The Chemistry 

of Pigments.' Pp. viii, 280. London, 1902. 
Russell, W. J., and Abney, W. de W., 'Action of Light 

on Water-Colours ' (Blue-Book). Pp. 78. Appendix 

of 14 diagrams. London, 1888. 
Solomon, Solomon J., * The Practice of Oil-Painting.' 

Pp. xvi, 278. London, 1910. 
Vasari, Giorgio, ' On Technique.' Translated by Louisa 

S. Maclehose ; edited and annotated by Professor 

G. Baldwin Brown. Pp. xxiv, 328. London, 1907. 



CONTENTS 



PAGB 

INTilODUCTION - - - - - I 



PART I 

PAINTING-GROUNDS 

CHAPTER 

I. PAPER, VELLUM, IVORY - - - - 7 

II. PLASTER, GESSO, STONE, SLATE, ETC. - - 18 

III. PANEL - - - - - - 29 

IV. CANVAS - - - - - '34 

PART II 
VEHICLES AND VARNISHES 

V. OILS - - - - - - 45 

VI. RESINS, WAXES, AND SOLID PARAFFINS - 68 

VII. YOLK AND WHITE OF EGG ; SIZE ; GLUE - 84 

VIII. GUM, STARCH, DEXTRIN, HONEY, AND GLYCERIN 9 1 

IX. WATER-GLASS, LIME- AND BARYTA-WATER - lOO 

X. SOLVENTS AND DILUENTS - - - I06 

XI. SICCATIVES OR DRYERS - - - " 125 

XII. VARNISHES AND VEHICLES - - - I30 



XX CONTENTS 

PART III 
PIGMENTS 

CHAPTER PAGE 

XIII. WHITE PIGMENTS . . . . 14^ 
XIV. YELLOW PIGMENTS - - - "157 
XV. RED PIGMENTS - - - - 1 86 
XVI. GREEN PIGMENTS - - - - 212 
XVII. BLUE PIGMENTS - _ - - 226 
XVIII. BROV^N PIGMENTS - - - - 252 
XIX. BLACK PIGMENTS - - - _ 264 
XX. CLASSIFICATION OF PIGMENTS - " "74 
XXI. TABLES OF PERMANENT, FUGITIVE, AND ALTER- 
ABLE PIGMENTS - - - - 283 
XXII. SELECTED AND RESTRICTED PALETTES - 290 



PART IV 

METHODS AND RESULTS 

XXIIL PAINTING-METHODS - - - " 3©! 

XXIV. THE STUDY OF OLD PAINTINGS AND DRAWINGS 325 

XXV. CONSERVATION OF PICTURES AND DRAWINGS - 342 
XXVI. TRIALS OF PIGMENTS - - - "359 

INDEX ----- 383 



THE CHEMISTRY 
OF PAINTS AND PAINTING 



INTRODUCTION 

The materials employed by ' picture-makers' are now very 
numerous. Some of the old pigments, and painting-grounds, 
and methods, have indeed fallen more or less completely 
into disuse ; but, on the other hand, many new products, 
both natural and artificial, have been added to the resources 
of the artist, while several new processes of painting have 
been introduced, or old methods modified. Nowadays it is 
very seldom that a painter prepares for himself any one of 
the materials which he uses, generally accepting, without 
much hesitation and without examination, the paper, the 
canvas, the paints, the oils, and the varnishes which his 
colourman supplies, provided they respond, at first sight, 
to his requirements. True he has abandoned, not without 
regret, several of the mosttreacherous compounds by which 
his immediate predecessors were seduced. ' Pure scarlet ' 
he has given up ; he is shy of asphalt ; tobacco-juice and 
Spanish liquorice are no longer regarded as desirable 
water-colours. He may go so far as to reject chromate 
of lead, but he still employs the pigment called chrome 
green, or green cinnabar, for he does not know that the 



2 INTRODUCTION 

same chromate of lead enters largely into its composition ; 
and he still thinks that madder yellow is a sound paint, 
because it is called madder, while he rejects the yellow 
lakes, which are derived from the same source. His 
linseed oil is neither made from pure linseed, nor cold^ 
drawn ; his copal varnish may not have a particle of pure 
copal in it ; but both are taken on trust. I do not expect 
that artists should become chemists trained to test their 
materials, but they will place themselves in a position of 
comparative security by acquiring an elementary know- 
ledge of the origin, the composition, and the character- 
istics of the various products with which their works are 
constructed. An architect is expected to recognise the 
sound or unsound quality of the timber, the stone, the 
brick, the iron, with which the edifice he designs is 
constructed : why should the painter take everything on 
trust ? The purchaser of a picture ought not to be dis- 
tressed by doubts as to its stability. The concentration 
of the artist's attention on the definitely artistic side of 
his practice must, of course, be in no wise interfered 
with, but time may still be found for the acquisition of 
such knowledge of his materials as shall enable him to 
discriminate between the good and the bad. He may 
even try, with great advantage, a few simple experiments 
— experiments performed in a few minutes with the 
simplest apparatus, and with the most innocent of re- 
agents. These are the more necessary now that painters 
no longer buy their raw materials, or make their own 
paints, and oils, and varnishes, or prepare their own can- 
vases and panels. Before colourmen generally under- 
took such work, early in the seventeenth century, painters 
were eager after receipts, and, there can be no doubt, 
were ignorant of reasons : there was little exact science 



INTRODUCTION 3 

underlying their art. Yet it would be unfair to the best 
colourmen of the present day to assume that they do not 
endeavour to provide, as far as possible, sound materials. 
But they do not manufacture all they sell. They are not 
paper-makers, nor, as a rule, are they manufacturers of 
oils and varnishes. Many of the pigments they furnish 
are not of their own make. If, for instance, you inquire 
the source of the artificial ultramarine you purchase of 
your colour man, you will find that it has probably been 
made in a factory wholly devoted to the manufacture of 
that pigment. The production of this material can 
indeed be properly carried on only in special establish- 
ments thoroughly equipped for a peculiar and difficult 
work. In reality, this specialization ought to be, and 
generally is, advantageous, but it renders the position of 
the colourman somewhat difficult. He has to assume 
responsibility for the soundness and genuineness of many 
products of the history and preparation of which he 
knows little or nothing. 

This difficulty confronts him in many directions. I have 
known cases in which importers or manufacturers' travel- 
lers have offered to artists' colourmen speciously prepared 
but spurious pigments, such as madder carmine and rose 
madder made from artificial alizarin, ultramarine ash 
containing not a particle of the native lapis-lazuli, and a 
gold ochre owing its colour to a basic ferric sulphate 
instead of a hydrate. Then, too, some of the original 
localities of a few native earths, such as terre verte and 
raw umber, are practically exhausted, and most of the 
new sources yield products of inferior hue. Hence the 
temptation to * exalt ' the hue of the commercial article 
by some seductive though dangerous addition. 

After these introductory observations, I may refer the 



4 INTRODUCTION 

reader to the table of ccntents for the plan of the present 
book, and to the prefaces for the object with which it has 
been prepared. I would add, here, only this one remark, 
that the materials with w^hich a painting is constructed 
are described in definite order, beginning with the 
ground, then passing on to the medium and the pig- 
ments, not omitting the final varnish, and finally closing 
with a brief summary of methods of painting, and of the 
experimental studies by means of w^hich the conclusions 
given in the earlier portions of the volume have been 
reached. 



PART I 

PAh\TING-GROUNDS 

Chapter I.— Paper. Vellum, Ivory. Chapter II. — Plaster or Intonaco, 
Stone, etc. Chapter III. — Panel. Chapter IV.— Canvas. 



CHAPTER I 

PAPER, VELLUM, IVORY 

As paper is used as the painting-ground for the vast 
majority of works executed in water-colours, and as 
this method of painting offers but slight protection to the 
pigments employed against hostile influences, it becomes 
of the greatest importance to ascertain that no unneces- 
sary elements of danger are introduced in the paper itself. 
We will now proceed to consider briefly the sources and 
constituents of drawing-paper. 

Linen from the common flax (Linum usitatissimtim), and 
in the form of white rags, should be the basis of the pulp 
used in the making of sound drawing-paper. In actual 
practice the cheaper and weaker fibre of cotton (seed-hairs 
of Gossypium sp.) has almost entirely displaced flax, 
although during recent years a successful attempt has been 
made in England to produce a high grade of hand-made 
drawing-paper almost wholly composed of linen. Other 
vegetable fibres might, no doubt, be employed for this 
purpose. Thus, Japanese paper, prepared from the bast- 
fibres of the paper-mulberry {Broiissonetia papyrifera), were 
it made less absorbent by the introduction of a sufliciency 
of size, would probably become an efficient, strong, and 
durable substitute for linen-paper ; but at present linen- 
papers, cotton-papers, and papers made from a mixture 

7 



xviii BIBLIOGRAPHICAL NOTES 

Laurie, A. P., ' The Pigments and Mediums of the Old 

Masters.* Pp. xvi, 192. London, 1914. 
Moreau-Vauthier, Ch., « La Peinture.' Pp. xii, 322. 

Paris, 1912. 
Ostwald, W., * Letters to a Painter.' Translated from 

the German by H. W. Morse. Pp. viii, 162. 

Boston, U.S.A., 1906. 
Parry, Ernest J., and Coste, John H., *The Chemistry 

of Pigments.' Pp. viii, 280. London, 1902. 
Russell, W. J., and Abney, W. de W., 'Action of Light 

on Water-Colours ' (Blue-Book). Pp. 78. Appendix 

of 14 diagrams. London, 1888. 
Solomon, Solomon J., < The Practice of Oil-Painting.' 

Pp. xvi, 278. London, 1910. 
Vasari, Giorgio, * On Technique.' Translated by Louisa 

S. Maclehose; edited and annotated by Professor 

G. Baldwin Brown. Pp. xxiv, 328. London, 1907. 



CONTENTS 



INTRODUCTION 



PAGE 
I 



PART I 

PAINTING-GROUNDS 

CHAPTER 

1. PAPER, VELLUM, IVORY - 

II. PLASTER, GESSO, STONE, SLATE, ETC. 

III. PANEL - - - - 

IV. CANVAS - - - - 



7 

i8 
29 
34 



PART II 
VEHICLES AND VARNISHES 

V. OILS - - - - - - 45 

VI. RESINS, WAXES, AND SOLID PARAFFINS - 68 

VII. YOLK AND WHITE OF EGG ', SIZE ; GLUE - 84 

VIII. GUM, STARCH, DEXTRIN, HONEY, AND GLYCERIN 9! 

IX. WATER-GLASS, LIME- AND BARYTA- WATER - TOO 

X. SOLVENTS AND DILUENTS - - - I06 

XI. SICCATIVES OR DRYERS - - - * 1 25 

Xn. VARNISHES AND VEHICLES - - - I30 

xix 



XX CONTENTS 

PART III 
PIGMENTS 

CHAPTER PAGE 

XIII. WHITE PIGMENTS - - - _ 14^ 
XIV. YELLOW PIGMENTS - - - "157 
XV. RED PIGMENTS - - - - 1 86 
XVI. GREEN PIGMENTS - - - - 212 
XVII. BLUE PIGMENTS - _ . . 226 
XVIII. BROWN PIGMENTS - - - - 252 
XIX. BLACK PIGMENTS - - - _ 264 
XX. CLASSIFICATION OF PIGMENTS - " -74 
XXI. TABLES OF PERMANENT, FUGITIVE, AND ALTER- 
ABLE PIGMENTS - - - - 283 
XXII. SELECTED AND RESTRICTED PALETTES - 290 



PART IV 

METHODS AND RESULTS 

XXIII. PAINTING-METHODS . - - - 

XXIV. THE STUDY OF OLD PAINTINGS AND DRAWINGS 
XXV. CONSERVATION OF PICTURES AND DRAWINGS - 
XXVI. TRIALS OF PIGMENTS - - - - 

INDEX . . . . . 



301 



THE CHEMISTRY 
OF PAINTS AND PAINTING 



INTRODUCTION 

The materials employed by * picture-makers' are now very 
numerous. Some of the old pigments, andpainting-grounds, 
and methods, have indeed fallen more or less completely 
into disuse ; but, on the other hand, many new products, 
both natural and artificial, have been added to the resources 
of the artist, while several new processes of painting have 
been introduced, or old methods modified. Nowadays it is 
very seldom that a painter prepares for himself any one of 
the materials which he uses, generally accepting, without 
much hesitation and without examination, the paper, the 
canvas, the paints, the oils, and the varnishes which his 
colourman supplies, provided they respond, at first sight, 
to his requirements. True he has abandoned, not without 
regret, several of the mosttreacherous compounds by which 
his immediate predecessors were seduced. ' Pure scarlet ' 
he has given up ; he is shy of asphalt ; tobacco-juice and 
Spanish liquorice are no longer regarded as desirable 
water-colours. He may go so far as to reject chromate 
of lead, but he still employs the pigment called chrome 
green, or green cinnabar, for he does not know that the 



2 INTRODUCTION 

same chromate of lead enters largely into its composition ; 
and he still thinks that madder yellow is a sound paint, 
because it is called madder, while he rejects the yellow 
lakes, which are derived from the same source. His 
linseed oil is neither made from pure linseed, nor cold- 
drawn ; his copal varnish may not have a particle of pure 
copal in it ; but both are taken on trust. I do not expect 
that artists should become chemists trained to test their 
materials, but they will place themselves in a position of 
comparative security by acquiring an elementary know- 
ledge of the origin, the composition, and the character- 
istics of the various products with which their works are 
constructed. An architect is expected to recognise the 
sound or unsound quality of the timber, the stone, the 
brick, the iron, with which the edifice he designs is 
constructed : why should the painter take everything on 
trust ? The purchaser of a picture ought not to be dis- 
tressed by doubts as to its stability. The concentration 
of the artist's attention on the definitely artistic side of 
his practice must, of course, be in no wise interfered 
with, but time may still be found for the acquisition of 
such knowledge of his materials as shall enable him to 
discriminate between the good and the bad. He may 
even try, with great advantage, a few simple experiments 
— experiments performed in a few minutes with the 
simplest apparatus, and with the most innocent of re- 
agents. These are the more necessary now that painters 
no longer buy their raw materials, or make their own 
paints, and oils, and varnishes, or prepare their own can- 
vases and panels. Before colourmen generally under- 
took such work, early in the seventeenth century, painters 
were eager after receipts, and, there can be no doubt, 
were ignorant of reasons : there was little exact science 



INTRODUCTION 3 

underlying their art. Yet it would be unfair to the best 
colourmen of the present day to assume that they do not 
endeavour to provide, as far as possible, sound materials. 
But they do not manufacture all they sell. They are not 
paper-makers, nor, as a rule, are they manufacturers of 
oils and varnishes. Many of the pigments they furnish 
are not of their own make. If, for instance, you inquire 
the source of the artificial ultramarine you purchase of 
your colourman, you will find that it has probably been 
made in a factory wholly devoted to the manufacture of 
that pigment. The production of this material can 
indeed be properly carried on only in special establish- 
ments thoroughly equipped for a peculiar and difficult 
work. In reality, this specialization ought to be, and 
generally is, advantageous, but it renders the position of 
the colourman somewhat difficult. He has to assume 
responsibility for the soundness and genuineness of many 
products of the history and preparation of which he 
knows little or nothing. 

This difficulty confronts him in many directions. I have 
known cases in which importers or manufacturers' travel- 
lers have offered to artists' colourmen speciously prepared 
but spurious pigments, such as madder carmine and rose 
madder made from artificial alizarin, ultramarine ash 
containing not a particle of the native lapis-lazuli, and a 
gold ochre owing its colour to a basic ferric sulphate 
instead of a hydrate. Then, too, some of the original 
localities of a few native earths, such as terre verte and 
raw umber, are practically exhausted, and most of the 
new sources yield products of inferior hue. Hence the 
temptation to ' exalt ' the hue of the commercial article 
by some seductive though dangerous addition. 

After these introductory observations, I may refer the 



4 INTRODUCTION 

reader to the table of contents for the plan of the present 
book, and to the prefaces for the object with which it has 
been prepared. I would add, here, only this one remark, 
that the materials with which a painting is constructed 
are described in definite order, beginning with the 
ground, then passing on to the medium and the pig- 
ments, not omitting the final varnish, and finally closing 
with a brief summary of methods of painting, and of the 
experimental studies by means of which the conclusions 
given in the earlier portions of the volume have been 
reached. 



PART I 

PA INTING-GRO UNDS 

Chapter I. — Paper, Vellum, Ivory. Chapter II. — Plaster or Intonaco, 
Stone, etc. Chapter III. — Panel. Chapter IV. — Canvas. 



CHAPTER I 

PAPER, VELLUM, IVORY 

As paper is used as the painting-ground for the vast 
majority of works executed in water-colours, and as 
this method of painting offers but slight protection to the 
pigments employed against hostile influences, it becomes 
of the greatest importance to ascertain that no unneces- 
sary elements of danger are introduced in the paper itself. 
We will now proceed to consider briefly the sources and 
constituents of drawing-paper. 

Linen from the common flax (Linum usitatissimum), and 
in the form of white rags, should be the basis of the pulp 
used in the making of sound drawing-paper. In actual 
practice the cheaper and weaker fibre of cotton (seed-hairs 
of Gossypium sp.) has almost entirely displaced flax, 
although during recent years a successful attempt has been 
made in England to produce a high grade of hand-made 
drawing-paper almost wholly composed of linen. Other 
vegetable fibres might, no doubt, be employed for this 
purpose. Thus, Japanese paper, prepared from the bast- 
fibres of the paper-mulberry {Broussonetia papyrifera), were 
it made less absorbent by the introduction of a sufficiency 
of size, would probably become an efficient, strong, and 
durable substitute for linen-paper ; but at present linen- 
papers, cotton-papers, and papers made from a mixture 

7 



8 CONSTITUENTS OF PAPER 

of these fibres, are the only kinds with which water- 
colourists are practically concerned. 

During his explorations of Chinese Turkestan, Sir Aurel 
Stein recovered many examples of early manuscripts 
written on felted vegetable fibre, that is, paper. In the 
British Museum are two scraps of such paper, with 
Chinese writing, which must be dated somewhere between 
the years a.d. 25 and 220. They are the most ancient 
specimens of paper known to exist in the world. But the 
manufacture of linen-paper in Europe has not at present 
been traced back farther than the second half of the twelfth 
century. Mr. W. H. James Weale, formerly Keeper of 
the Art Library in the Victoria and Albert Museum, 
informed me that the two first paper-mills in France were 
set going near Ambert, in the valley of the Valeyre, by 
men who, during their captivity in the Holy Land, were 
forced to work at the manufacture of paper at Damascus. 
One of these French mills was called ' Damascus,' the 
other ' Ascalon.' This was previous to the year 11 89. 
To Mr. Weale I am also indebted for an opportunity of 
examining two early specimens, obtained from the ' Regis- 
tre des Revenus de I'^^veche du Puy.' As one of the 
sheets contains contemporary entries of the year 1273 — 
the other entries belonging to 1289 — these papers are, at 
least, as early as the years named. Both papers present 
the creamy hue, the translucency, and the gloss of vellum. 
One hundred square inches of the earlier specimen weigh 
127 grains ; of the later, 163. Both are heavily sized with 
paste made from wheaten starch. The use of starch for 
sizing paper has been revived of recent years, but animal 
size or jelly is still extensively employed. Some paper is, 
indeed, made from felted linen pulp alone without size ; 
but it is blotting or filter paper, and is quite unfitted for 



ANAL YSIS OF DRA WING -PA PER 9 

water-colour work, for when a wash of pigment is passed 
over it, the colouring matter and the water partially separ- 
ate, while the outline of the brush-stroke is not preserved. 
Before entering further into the question of what are 
the essential and what the accidental and unnecessary con- 
stituents of paper, I give the summarized results of six 
analyses, which show the percentage proportions found in 
good samples : 

ANALYSES OF DRAWING-PAPERS 





Water 


Size 


Ash 


Fibre 


Hodgkinson, 1869 - 


68 - 


4-6 . 


II 


■ 87-5 


English, 1876 - 


10-9 


61 • 


II 


. 81 -9 


Dutch, 1876 - 


I I'D 


4-8 . 


0-9 ■ 


■ 83-3 


Whatman. 1885 - 


7*4 - 


6-3 ■ 


i-i 


. 85-2 


Arnold, 1894 - 


74 - 


7-6 ■ 


■ 1-5 


- 835 


'O. W.,'1897 


87 - 


5'5 ■ 


17 ■ 


. 84-1 



Water.— It should be noted that the percentages of 
water shown in these analyses vary considerably by reason 
of variations in the humidity, temperature, and pressure of 
the atmosphere to which the different papers had been 
exposed just before the analyses were made. There are, 
however, slight permanent peculiarities in samples made 
from different fibres or sized in different ways ; in conse- 
quence the moisture-absorbing and moisture-retaining pro- 
perties of different papers are not precisely identical under 
identical atmospheric conditions. This hygroscopic mois- 
ture does, indeed, vary inversely with the temperature, and 
directly with the amount of water- vapour in the air ; it is 
increased also by an increased barometric pressure. There 
is no doubt that if it could be wholly excluded, the larger 
number of changes which occur in the pigments of a water- 
colour drawing would be prevented. It is most injuriously 
active when a framed drawing is exposed to considerable 



10 ASH OF PAPER 

ranges of temperature. Under these conditions the 
moisture of the paper is first partly turned into vapour, 
then condensed on the glass, and, lastly, is re-absorbed by 
the paper, and, for a time, especially by the pigments lying 
on its surface. This temporary condensation of an excess 
of moisture upon the coloured surface does much injury 
before hygroscopic equilibrium is once more re-estab- 
lished. Much less harm would accrue were the vapour- 
ized water allowed to escape. 

Size. — The size must be considered next. It may be 
applied to the pulp or to the sheet, and may consist of 
gelatine with a little alum, of colophony or rosin dissolved 
in soda-lye, followed by treatment with alum or alum-cake. 
Sometimes starch is used along with alum or alum-cake. 
From good drawing-papers, which are sized in the sheet 
with animal size, the greater part of the size may be ex- 
tracted by means of boiling distilled water, the solution 
being usually neutral or faintly acid, sometimes faintly 
alkaline, to test-papers. Gelatine and starch, to the extent 
of about 5 per cent, of the weight of the paper, are the 
safest sizing materials. 

Ash. — The ash or mineral matter in paper may be 
derived from three sources, namely, traces of the original 
mineral substances taken up by the flax plant from the 
soil, and still remaining associated with the felted pulp; the 
mineral matters, such as soda and alum, introduced with 
the size; and, lastly, the mineral compounds used to whiten, 
to weight, or to finish the paper, or in bleaching the fibre 
and as * antichlors.' In common and adulterated papers 
the ash greatly exceeds i per cent., twelve parts per hun- 
dred of paper being no unusual proportion. This * filling ' 
may contain or consist of the following substances : kaolin 
or china-clay, silicate of lime or 'pearl-hardening,' chalk or 



FIBRE OF PAPER ii 

whitening, lead-white, baryta white or * white dressing,' 
artificial gypsum or ♦ satin-dressing,' and a mixture of alu- 
minium hydrate with magnesium carbonate or with calcium 
carbonate, known as * satin-finish * or * satin-white.' Other 
substances which increase the amount of ash left when a 
paper is burnt are blue colouring matters, introduced to 
counteract the natural yellow tint of the pulp. These 
include artificial ultramarine, smalt or cobalt blue, and 
Prussian blue. 

Fibre. — What is put down as fibre in the analyses of 
paper previously cited, is a substance, or group of sub- 
stances, to which the name of cellulose is given by 
chemists. Cellulose consists of the three elements — 
carbon, hydrogen, and oxygen ; it is, when pure, entirely 
combustible, leaving no ash. 

The source of this cellulose is by no means without in- 
fluence on the durability, strength, and working quality of 
drawing-paper. The fibres of linen and of cotton present 
distinct differences of form and resistance to strain. When 
working on a paper with a knife so as to develop high lights, 
the water-colour painter soon discovers the weakness and 
fluffiness of abraded cotton, while the clear-cut surfaces of 
linen are equally obvious. Even in washing and in taking 
out lights from a drawing by sponging and rubbing, the 
superiority of linen-paper to cotton-paper is very marked; 
in fact, papers into which a high proportion of the latter 
fibre enters will not stand much worrying. The other 
fibrous materials commonly forming the basis of ordinary 
papers are, on one score or another, less desirable than 
cotton. Nearly all of them require, in order to fit them for 
paper-making, a very drastic treatment, which is liable to 
leave behind it traces of injurious chemicals, or to yield 
altered material of lessened strength and permanence. 



12 PAPER-MAKING 

Wood-pulp, esparto, and straw-pulp belong to this cate- 
gory. 

Paper-making. — The technology of paper-making cannot 
be discussed here, but a few references to the chemicals 
employed in the process of manufacture may be usefully 
given at this point. Amongst these chemical substances, 
one or more of which will have been introduced into the 
fibrous basis of the paper or into the size may be named: 
caustic soda and caustic lime ; chloride of lime, magnesium 
hypochlorite, moist chlorine gas, and sulphuric acid ; 
alum, aluminium chloride, and aluminium sulphate ; 
sodium sulphite ; gelatin. Of course, it is possible to 
cleanse and bleach the higher class of rags without 
having recourse to any chemical treatment, but the 
' souring ' with sulphuric acid and the employment of 
some soda or sodium carbonate to remove grease are 
usual ; while there is always a salt of aluminium present 
in the size. Indeed, in the best and purest drawing- 
papers, the alum, or its equivalent, is the one ingredient 
upon which the chemist interested in painting will look 
with suspicion. But the subject of the presence of chemi- 
cals, injurious or innocuous, in the finished product of the 
paper-mill may be relegated to the following paragraphs. 

Paper-testing. — The simplest test of the suitability of 
any sample of drawing-paper for water-colour work con- 
sists in applying to its surface uniform and weak washes 
of a chosen set of sensitive pigments. A sound standard 
paper is taken for comparison ; this may be ' Whatman,' 
but it should be first swilled in cold distilled water for 
five minutes, and then hung up to dry. In applying this 
test, a strip of the sample to be tested and one of the 
standard paper should be laid side by side, and then the 
several colour washes, made with distilled water, carried 



TESTING PAPER 13 

across both strips by means of a broad brush. The pig- 
ments used may be French ultramarine, chrome yellow, 
and carmine. Unless they are employed in very dilute 
admixture, the changes produced by alum and other 
chemicals will not be perceptible. There should be no 
bleaching of the ultramarine or the carmine, or any 
blueing of the latter, and no dulling of the chrome, even 
after the lapse of a week from the date of the experiment. 
Washes of tincture of azolitmin from litmus^ tincture of 
dahlia flowers, and tincture of methyl-orange may be 
similarly applied to paper-strips ; in this case it will prob- 
ably be found that the two former tests will show an 
acid reaction, and the methyl-orange a basic or alkaline 
reaction. This seemingly strange result has been found to 
arise from the presence of a derivative of the alum in the 
size, namely, an aluminium sulphate which is acid to some 
tests and basic to others. This point has been established 
by the experiments* of Messrs. Cross and Bevan, Mr. C. 
Beadle, and Drs. P. N. Evans and Quirin Wirtz, who have 
proved that all the drawing-papers of well-known makers 
which they have examined contained no free sulphuric 
acid. Of course, the question remains, * How far, if at all, 
is the basic aluminium sulphate in drawing-paper injurious 
to sensitive pigments ?' This inquiry can, I think, be an- 
swered by applying the colour-tests already described, not 
only to the suspected papers themselves, but also to extracts 
from them made with cold distilled water and also with hot. 
Other useful tests are the following : 

1. Burn 100 grains of paper to a white ash ; not more 
than I '5 grains of incombustible residue should be found. 

2. Extract 100 grains of paper repeatedly with boiling 

• * Journal of the Society of Chemical Industry {1892), pp. 212, 213, 
261. 



14 TESTING PAPER 

distilled water. The united watery extracts, evaporated 
to dryness, should not amount to 8 grains. 

3. If straw or esparto fibre be present in a paper, it will 
become red when immersed in a boiling i per cent, solution 
of aniline sulphate. 

Attempts have been made to size paper with casein dis- 
solved in ammonia, and also with ' viscose,' a modified 
cellulose made out of the substance of the paper itself by 
means of water, caustic soda, and carbon disulphide. At 
present, however, gelatin-sizing holds its own. The neces- 
sity of introducing alum, or an equivalent of some other 
aluminium salt, into this size is its chief drawback, although 
an animal product of the group to which gelatin belongs, 
being prone to decomposition and to the attacks of micro- 
scopic organisms, itself constitutes a source of danger. 
Alum is used not merely as an antiseptic, but because it 
exerts a peculiar liquefying effect upon the size. A little 
alum solution added to gelatin solution increases its stiff- 
ness, but further additions up to an easily ascertained point 
make the solution more mobile. It is absolutely necessary 
to keep the alum percentage low ; I found in a batch of 
one well-known make of drawing-paper that exactly twice 
as much alum had been employed as was necessary. My 
remonstrance with the manufacturers had its due effect. 

The roughness or smoothness of the surface of the paper, 
or cardboard, is not without influence on the permanence of 
water-colours. The pigments become less intimately asso- 
ciated with the smooth surface of a hot-pressed paper than 
with a comparatively rough natural surface. The rough 
surface is, however, liable to wider and more rapid fluctua- 
tions in the amount of hygroscopic moisture. 

Some apparently sound papers deteriorate in strength 
and tint on being kept. Such changes may occur even when 



SIZE IN PAPER 15 

pure linen rags have been used for the pulp ; they may be 
generally traced to the disintegrating action on the fibre of 
the chemical bleaching agents employed. The development 
of rust-spots, when not due to the mount or backing of a 
drawing, arises from the presence of small particles of 
metallic iron from the machinery having become em- 
bedded in the pulp. These particles appear grey, brown, 
or black ; they may be detected by placing a drop of oxalic 
acid solution on the suspected spot, allowing it to dry, and 
then moistening the place with a drop of a freshly-pre- 
pared solution of tannin. If the particle be iron an ink- 
stain will be produced. However, some dark spots con- 
sist of blackened grease, or of tar, or of the paper-fungus 
{Myxotrichum chavtanim). 

Naturally, there is a small quantity of oil or fat in 
paper ; it varies from 3 to 5 parts in a thousand. The 
difficulty experienced in immediately wetting a surface of 
paper, caused by the presence of this trace of oil, may be 
overcome by first washing the surface with distilled water 
to which a drop or two of caustic ammonia has been added. 
A solution of the natural mixture of alkaline organic salts, 
known as oxgall, effects the same purpose. The use of 
borax had better be avoided. It is always advisable to 
wet the whole surface of the paper before beginning a 
water-colour drawing. Thus any abrasions or defects of 
the surface will become apparent. 

As drawing-papers are sized in the sheet they occasion- 
ally show a peculiar defect arising from the irregular dis- 
tribution of the size. In such cases, when the surface is 
scraped off, an absorbent layer of imperfectly sized pulp is 
revealed beneath. When such paper is used for water- 
colour painting the sinking-in and running of the pigments 
produce disastrous results ; but it is easy to guard against 



i6 VELLUM AND IVORY 

accidents of this sort by previously scraping and colouring 
a corner of the sheet to be used. The peculiarity is gener- 
ally owing to the too prolonged and slow drying of the 
sheets of paper after they have been removed from the 
warm sizing-bath and pressed. The solution of size is 
brought to the surfaces from the interior of the sheet, and 
remains there. Moreover, in very slow drying, the size is 
apt to decompose with loss of its glutinous character and, 
possibly, the formation of mildew. A good drawing-paper 
will indeed have rather more size at the surface than in 
the interior, this result being secured by a rate of drying 
which is neither too rapid nor too slow. Let us add that 
the strength of paper when completely wetted and in the 
presence of free water, is very low. If, however, it has 
been gelatin-sized and afterwards sprayed with a 40 per 
cent, solution of formalin to coagulate the gelatin it be- 
comes appreciably stronger. 

As to vellum, parchment, and ivory, little need be said. 
All three contain the characteristic ingredient ossein, an 
insoluble nitrogenous organic substance, which by long 
boiling with water is converted into gelatin : a solution of 
gelatin constitutes ordinary size. Water-colour paints 
placed upon any of these materials sink either very 
slightly, or not at all into their substance — a very few, 
such as aureolin, strontia-yellow, and madder carmine, 
stain the superficial layer. The old method of preparing 
vellum for the reception of water-colours consisted in 
rubbing the surface with very finely-ground bone-ash, or 
with pulverized sandarac. Pumice-stone or cuttle-fish, re- 
duced to a minutely divided state by pounding, grinding, 
and sifting, may be used for this purpose ; the infusorial 
earth known as polishing silica, or kieselguhv, may also be 
employed. 



VELLUM AND IVORY 17 

Ivory which has become yellowish through age and se- 
clusion from light may be safely bleached by contact with 
an ethereal solution of hydrogen peroxide. The treatment 
is best carried out in a wide-mouthed stoppered bottle, 
care being taken to immerse the sheets of ivory wholly in 
the liquid, and not to allow them to touch each other. 

Much care is necessary in selecting tinted and coarse 
coloured papers for water-colour work. The tints of the 
former are often obtained by the introduction of fugitive 
pigments into the pulp ; the latter are often made of in- 
ferior and mixed fibres, and sometimes contain lead- white 
and other m]\iy:\ous fillings. 'Turner' paper, for example, 
owes its grey-blue tint to the presence of indigo, while 
* Varley' paper contains about 20 per cent, of 'mechanical' 
wood-pulp, a material which steadily darkens into brown 
after but a short exposure to light. ' Sugar ' paper, what- 
ever its hue, should be avoided. Mill-board is often 
made of wood-pulp, oakum and straw-pulp : its surface is 
primed for oil-painting in the same way as canvas. 



CHAPTER II 

PLASTER, GESSO, STONE, SLATE, ETC. 

The painting-grounds to be considered in this chapter 
consist mainly of mineral substances. However their con- 
stituents may be varied, in accordance with the process to 
be used in painting upon them, the wall or backing upon 
which they are spread should fulfil certain conditions. It 
must be naturally dry, free from soluble saline matters, and 
not very porous. A damp-proof course above the level 
of the ground is necessary, and the wall should be well- 
built, and free from tremors. A double wall well-bonded 
has been recommended : in this case the air enclosed 
between its two divisions should not be stagnant. 

Before being plastered, the wall, whether its surface be 
of stone, bricks and mortar, roughened slate, or tiles, must 
be thoroughly wetted with lime or baryta-water. The 
plaster is applied in two or more coats, the coarsest and 
thickest first. In the case of a ground for fresco the two 
ingredients usually employed are (or rather were) pure 
slaked lime, and clean sharp silicious sand. The sand 
must be uniform in grain, white, and free from soluble 
salts. The slaked lime is so important an ingredient in the 
majority of plasters, that it is expedient to describe its 
preparation once for all. Before doing so we may state 
the relations subsisting between the three compounds 
known generally as carbonate of lime (chalk), or mild Hme, 

i8 



COMPOUNDS OF LIME 19 

burnt lime, or quicklime, and slaked lime. The first of 
these is neutral and nearly insoluble in pure water, the 
second and third are alkaline and caustic. When burnt 
lime unites with water to form slaked lime it becomes 
slightly soluble in pure water. In chemical language these 
three compounds are called respectively calcium carbon- 
ate, calcium oxide, calcium hydrate (or hydroxide). From 
the first substance the others are readily obtained. If 
calcium carbonate, often called carbonate of lime, be 
heated to a sufficient temperature, it is decomposed, being 
resolved into carbon dioxide (carbonic acid gas) which 
escapes, and calcium oxide (lime) which remains : from 
100 parts by weight of the carbonate 56 parts of lime, that 
is, burnt lime, are obtained. Placed in water or exposed 
to moist air this burnt lime combines with water, 56 parts 
of it uniting with 18 parts of water to yield 74 parts of 
slaked lime, calcium hydrate. In the ordinary country 
atmosphere, which contains no more than 3 measures of 
carbonic acid gas per 10,000, slaked lime or calcium 
hydrate loses its combined water, slowly becoming once 
more the carbonate from which it was originally produced : 
74 parts of hydrate lose 18 parts of water and combine 
with 44 parts of carbonic acid, and yield 100 parts of car- 
bonate. Thus mild lime is formed once more from caustic 
lime. By this change, if it be effected in the presence of 
a sufficiency of free water — that is, if the hydrate of lime 
be in the state of a firm paste — the whole substance 
becomes a hard crystalline solid, like an opaque marble. 
Advantage may be taken of this hardening or cementing 
process to firmly incorporate other substances with the 
lime, Silicious sand, infusorial earth, pumice, marble 
powder, and many other mineral substances, may be thus 
introduced. Such of these materials as are silicious may 



20 LI ME- PUTTY 

contain silica in a form which is known as ' soluble silica.' 
This substance further strengthens the plaster by forming 
with a part of the lime an insoluble compound called sili- 
cate of lime. To return to the preparation for artistic 
purposes of hydrate of lime. White or black marble, 
limestone, chalk, or other fairly pure forms of carbonate 
of lime are first of all hurnt, and then the quicklime pro- 
duced is slaked with clean water. This is done in a 
grouting box, having a sluice i or 2 inches from the bottom. 
Run the thick cream of lime into a tank of slate and keep 
it, covered loosely, for two months. At the end of this time 
it will be ready for all the rougher purposes of plastering. 
For finer work the grouting operation is to be repeated, and 
the cream of lime strained through hair-sieves, and pre- 
served in screw-top stoneware jars. Some water will accu- 
mulate above the lime-putty, as it may be called, in these 
jars ; it should be poured off or drawn off, from time to 
time. The jars are kept tightly closed to prevent further 
carbonation of the lime hydrate. This change, if carried 
beyond a certain point, is undesirable, since the binding 
and hardening powers of the lime would thereby be 
lessened seriously, or even vanish altogether by its con- 
version into mild lime : not more than one-third or at most 
two-fifths of the lime should be converted into the car- 
bonate. The lime-putty thus prepared may be used for 
plaster and intonaco with the certainty that it will not give 
rise to defects in the painting-grounds made therewith. 
Much lime paste of this kind was prepared for the works 
in fresco in the Houses of Parliament, and was kept in 
the cellars under that building, where probably some of 
it still remains. I have made many experiments with 
samples from that source, and can speak with confidence 
of its excellent quality. 



FRESCO GROUNDS 21 

Btion' Fresco. — A good mixture for the first application to 
the moistened wall consists of 2 parts (by weight) of clean 
sharp sand to one of lime-putty. When one or more coats 
of this mixture have been duly laid and have set, then the 
surface is ready to receive the final coat or intonaco, the 
actual painting-ground. Before this is applied, the rougher 
plaster below must be thoroughly wetted with distilled or 
lime water. The sand in the intonaco is of finer and more 
uniform grain than that previously employed; the intonaco 
itself is only one eighth of an inch in thickness. All the 
coats must be laid without having recourse to scraping or 
* floating' ; the latter operation brings too much lime up to 
the surface. Considerable practice and manual dexterity 
are needed in these operations. The work of painting is 
at once commenced when the intonaco has been laid, no 
more being spread at one time than the artist can cover in 
the day. Upon the wet soft plaster the cartoon is laid, and 
the outlines and other important parts pounced in, trans- 
ferred, or impressed by an ivory point. Rapidity and 
firmness of execution, with the distribution of a uniform 
thickness of pigment, are matters to which special atten- 
tion must be paid. The chemistry of this method of 
painting will be discussed in Chapter XXIII. 

Many modifications in the preparation, proportions, and 
materials of fresco painting-grounds have been introduced 
or suggested from time to time. I have found the following 
mixture to yield an excellent plaster for this purpose : 
Three parts of burnt lime in very fine powder are ground 
up with 2 parts of whitening or prepared chalk ; the mix- 
ture is grouted, and then strained through hair-sieves ; 
5 parts of the putty thus obtained are mixed with 5 parts 
of sifted crushed marble, or with 5 parts of sharp, fine, 
sifted sand, or with 3 parts of sifted pumice, or with the 



22 TEMPERA GROUNDS 

same quantity of infusorial (silicious) earth ; the whole 
being moistened with a sufficient quantity of lime-water 
to render working easy. For the undercoats the sand, etc., 
introduced may be coarser ; while a small quantity of the 
most silky and whitest asbestos, cut with scissors into 
short uniform lengths, will prove a desirable addition. 
The asbestos * lessens the risk of any lack of continuity 
in the undercoats. 

Fresco-Secco and Tempera. — For fresco-secco the same 
ground as that required for true fresco may be used, but it 
is allowed time to dry and harden. So long as it contains 
any caustic lime this ground is unfitted for work in tem- 
pera, as its alkaline nature seriously limits the variety of 
pigments which may be employed in this method. When 
carbonation of the lime is complete it may be employed 
for tempera-painting, the surface being first treated with 
warm size. Many Greek and Byzantine paintings were, 
however, executed upon a caustic lime ground, but the 
pigments employed consisted chiefly of those natural 
earths which are unaffected by alkalies. In these Greek 
tempera-grounds slaked lime mixed with chopped straw, 
flax, or cotton, formed the basis of the plaster. It is 
scarcely necessary to remark that these vegetable 
materials are liable to decay and to cause discoloration 
of the ground. 

The ordinary ground for Italian and Spanish tempera- 
paintings consisted either of whitening and size, or of 
burnt gypsum (that is, plaster of Paris), stirred well with 

* Professor Laurie, in his ' Materials of the Painter's Craft ' 
(p. 138), attributes this recommendation as to the use of asbestos 
to Mr. James Ward, who names it in his book on ' Fresco Painting ' 
(p. 14) published in 1909. But the present author published the 
same recommendation with fuller instructions in the year 1890 : it 
will be found on p. 18 of the first edition of the present handbook : 
but he also may have been anticipated. 



TEMPERA GROUNDS 23 

water so as to lose the power of setting, strained, and 
mixed with size. Sometimes both whitening and slaked 
burnt gypsum are found together as constituents of the 
ground. The ground was laid directly on the panel, or 
on the cloth which had been previously glued to the 
wood. Great care was taken by sifting and washing to 
secure the fineness and purity of the whitening (calcium 
carbonate) and of the slaked plaster of Paris (calcium 
sulphate united with two proportions of water). Various 
kinds of size were used ; one of the best was made partly 
from parchment, partly from the finer kind of fish-glue. 
An excess of size will cause the ground to crack ; it must 
never contain such a quantity as to be rendered non- 
absorbent. All tempera-grounds of gesso were originally 
absorbent ; in course of time they have become more so 
owing to the decay of the size. Whether they were 
afterwards to be painted in tempera or oil they were 
always first sized. This sizing preserved the luminous 
whiteness of the ground, which was unable to absorb the 
oil of oil-paints or that present in the egg-yolks employed 
in tempera. A proof of the existence of this layer of size 
above the ground proper is obtained in the process of 
transferring old tempera and oil pictures to canvas, for 
in such cases we find discoloration of the ground under 
cracks only where both the size and the paint above it 
have become fissured. 

It will have been gathered from what has been stated 
in the preceding paragraph that a non-caustic tempera- 
ground is suitable for work in oils. In the latter case, 
however, it must be perfectly dry before the painting is 
commenced. It should be gently warmed and rubbed 
with a little clean spirits of turpentine before laying on 
the first coat of oil-paint. 



24 STEREOCHROME GROUNDS 

Steveochromy. — The ground for stereochromy has been 
modified several times since the first introduction of this 
method of water-glass painting. Originally it was recom- 
mended to use an undercoat containing 2 parts of sharp 
sand, 2 parts of fine sand, and i part of slaked lime in 
fine powder. Upon this was laid an intonaco of one-tenth 
to one-eighth of an inch in thickness, made of 3 parts of 
fine sand and i part of slaked lime. The fineness or 
coarseness of the sand in the intonaco must, however, be 
regulated by the nature of the surface required by the 
artist. I see that nearly fifty years ago I recommended* 
the employment of sifted white marble powder, and of 
several other substitutes for sand, recommendations 
which, within the last few years, have been again brought 
forward by Herr Adolph Keim. Oxide of zinc may be 
advantageously substituted for a part of the lime in the 
intonaco, and it may be added to the pigments. Keim 
recommends the wall to be first coated with a mixture of 
I part of burnt lime (which is to be slaked with distilled 
water), and 4 parts of a composition consisting of coarse 
quartz sand, infusorial earth, and powdered marble. The 
actual painting-ground, which is from one-eighth to a 
quarter of an inch in thickness, is made of i part of 
slaked lime, and 8 parts of a mixture of the finest quartz 
sand, marble sand, marble meal, and infusorial earth. 
Fine asbestos paper, wetted with lime-water, and firmly 
pressed by rolling into a soft freshly-laid lime and sand- 
plaster, makes an excellent ground for stereochrome 
painting ; but as a single breadth only of this paper can 
be used, the size of the work that can be executed 
upon it is somewhat limited. All the precautions as to 

* 'Chemistry of the Fine Arts' in Cassell's 'Technical Edu- 
cator.' 



SPIRIT-FRESCO GROUNDS 



25 



dryness of the wall and purity of the materials, already 
noted in the case of fresco-grounds, must be observed in 
reference to those intended for stereochrome painting. 

Spirit-Fresco. — The ground recommended by the late 
Mr. Gambier Parry for that modified form of varnish- 
painting to which he gave the name of * Spirit-Fresco ' is 
identical with that required for true fresco. All the usual 
precautions as to the dryness of the backing, and its 
freedom from soluble salts, must be taken. The plaster 
must be allowed to dry completely before the operation of 
saturating it with the medium is commenced ; the lime in 
it should also have become mild — that is, carbonated. 
(See Chapter XXIII. for tests for alkalinity and moisture.) 
Syringing the plaster with distilled water previously 
charged under pressure with carbonic acid gas, though 
it delays the drying, hastens the carbonation of the lime 
materially. To complete the preparation of the ground, 
it should, when quite dry, be soaked with a mixture of 
two parts of the medium (Chapter XII.), and three of tur- 
pentine. After two days, this treatment must be repeated. 
A third application may be needed for very porous 
grounds. Another period of forty-eight hours having 
elapsed, the surface receives a coat of white paint, made 
of equal parts of white lead and gilder's whitening, 
ground up with the medium diluted with one-fourth or 
one-third its bulk of turpentine. This priming is re- 
peated when the first coat is dry. After three weeks, the 
painting may be commenced. Stone and terra-cotta, if 
sufficiently porous, may be primed in the same way as 
plaster. Under no circumstances should cements con- 
taining plaster of Paris be introduced into the grounds 
used for spirit-fresco. 

During the last twenty years a considerable number of 



26 SLATE AND STONE 

large mural paintings have been executed either in Gam- 
bier Parry's medium or in the paraffin-copal medium. 
Some of these works have been painted directly on 
plastered walls, some on canvases which have been 
afterwards affixed by marouflage to the surfaces prepared 
to receive them. To the latter category belong nearly 
all the paintings in the Ambulatory of the Royal 
Exchange, London. Each of the compartments has 
been very carefully arranged with a view to secure dry- 
ness and freedom from soluble saline matter. In front 
of the wall itself has been fixed a slate slab slightly 
inclined forwards at the top and having a ventilated air- 
space behind it. Upon the slate the finished picture has 
been attached (or maroufle) by means of a thick paste of 
white-lead, oil, and copal-varnish, spread not only upon the 
slate, but simultaneously upon the back of the canvas. It 
may be affirmed that paintings so secured are free from all 
risk of injury from the back. In an atmosphere like that 
of London the surface of the painting must either be pro- 
tected by glass or be periodically cleansed from deposits 
of dust, soot, tarry matters, and the other impurities 
which are described in Chapter XXV. of this handbook. 
Several fresh materials have been recently employed as 
painting-grounds. They are either patent or secret pre- 
parations, dependent in general for their solidification upon 
reactions between insoluble earthy and alkaline earthy 
matters, such as china-clay, asbestos, and compounds of 
lime and magnesia, with solutions of such salts as mag- 
nesium chloride, aluminium sulphate, and alum. There is 
sometimes a lack of tenacity, and always a lack of tough- 
ness in these mixtures, but some artists find them to pos- 
sess precisely the texture and absorptive character they 
desire in grounds not only for tempera, but also for oil- 



SLATE AND STONE 27 

painting, and they may be spread on canvas as well as on 
more rigid supports. There is some danger of want of 
adhesion between the paint and the ground. It is also 
necessary to make sure that the materials of the ground 
do not affect sensitive pigments such as ultramarine. The 
hardening or petrifying liquids which in most cases are 
used in association with solid preparations to make the 
grounds in question, are invariably acid to test-paper, 
unlike the alkaline silicates described in Chapter IX. 

Slate may be used as the ground for spirit-fresco and oil- 
painting ; but its freedom from crystals of iron-pyrites, 
which present a brass-yellow colour, must be first ascer- 
tained. The firm adhesion of any priming, or other layers 
of oil-paint which may be applied subsequently, to slate 
may be secured in the following manner. The slate is 
slowly warmed in a water-oven, and thus becomes quite 
dry. While still warm, it receives a very thin coat of 
oil-copal varnish, largely diluted with turpentine or with 
toluol, and applied warm. When this film is hard, the 
painting may be carried out as in the ordinary way of 
using oil-colours ; a priming of flake-white ground in oil 
and mixed with a little copal- varnish and turpentine, may 
be first applied, if desired. Terra-cotta and stone may be 
treated in the same way, but, being more absorbent than 
slate, the process recommended on p. 31 is preferable. 

Owing to the presence of sulphuric acid in urban air 
painting-grounds containing calcium carbonate are liable 
to an injurious change, the carbonate being turned in 
part into the hydrous sulphate (gypsum) with a consider- 
able increase of bulk. Then, through such expansion, 
the surface-pigment becomes fissured and even detached. 
It will be readily understood that grounds consisting 
chiefly of sulphate of lime are not susceptible of such 



28 SLATE AND STONE 

change. So, where damp can be excluded, they may be 
used for mural paintings, ground flints or fine sand being 
admixed with the burnt gypsum employed. The paint- 
ings of the buried cities of Chinese Turkestan explored 
by Sir Aurel Stein were executed on grounds of this kind 
— grounds, that is, of nearly pure plaster of Paris. 



CHAPTER III 

PANEL 

Wood, as a backing for the painting-ground of works in 
tempera and oil, presents some advantages over plaster and 
canvas. Its chief merit lies, perhaps, in its comparative 
immunity from mechanical injuries. The wood selected 
must be hard, that its surface may resist blows and abra- 
sion ; and it must not contain much resin, gum, colouring- 
matter, or other ' extractives,' as they are called, or else 
discoloration of the painting-ground, or priming, may 
occur. Wood grown in poor soils, in temperate climates, 
and felled in winter, is the best. The Flemings used oak ; 
the Italians white poplar. But oak often proves treacher- 
ous, through irregular sh mkage; while poplar is too soft. 
Italian painters employed, also, the wood of the stone 
pine and chestnut. Leonardo da Vinci recommended 
cypress, pear, and service-tree. Mahogany, which was 
unknown to the old painters, is now generally employed. 
Teak and cedar, and also American or black walnut, 
deserve further trial. 

The specific gravity of wood varies from 0-3 to 1-3 ; the 
lighter kinds contain large volumes of interstitial air. 
The longitudinal contraction of wood is much less than 
the transverse ; the distribution, form, and number of the 
cracks in old panel-pictures is often to be traced to this 

cause. 

29 



30 PANEL 

Wood contains (i) water, (2) ligno-cellulose, (3) extrac- 
tives, (4) ash or mineral matter. The water, in thoroughly- 
seasoned and air-dried wood, generally constitutes about 
one-eighth part of its weight. The main constituent of 
wood is the so-called ligno-cellulose, which is present to 
the extent of from 75 to 85 per cent. It may be resolved 
into two substances, which, for convenience' sake, are here 
called cellulose and lignose. The extractives belong to 
two groups — one, soluble in alcohol and ether, consists 
chiefly of resins ; the other, soluble in cold or hot water, 
or else in very dilute alkalies, includes tannin, albu- 
minoids, gum, and colouring-matters. The following 
analyses of three kinds of wood in an air-dried state will 
convey a fair idea of their constitution in 100 parts : 





Mahogany 


Oak 


Pine 


Water - 


■ 124 - 


- 131 - 


. 12-9 


Cellulose 


490 - 


- 39-5 - 


- 533 


Lignose - 


276 - 


■ 343 - 


- 28-2 


Ash 


i-i - 


I '2 - 


- 0-3 


Resin 


I'O - 


- 0-9 - 


- 1-6 


Water-extract 


8-9 - 


- I I'O - 


- 37 



The preparation of panels for painting requires much 
time and trouble. The directions given by ancient authori- 
ties are numerous, and not always accordant. One author 
tells us to boil the wood ; another says we are to coat it 
with mastic dissolved in twice-distilled turpentine and 
mixed with white. Then it is to be treated twice or thrice 
with spirits of wine, in which some white arsenic or corro- 
sive sublimate has been dissolved ; coats of boiled oil, of 
liquid-varnish* and white, and of verdigris and yellow are 
subsequently mentioned. Probably the best method of 
treating the harder woods intended for pictures is, after 

* Made by boiling i part of sandarac in 3 parts of linseed-oil. 



PREPARATION OF PANELS 31 

thorough seasoning, first of all to reduce the panel, by 
planing and glass-papering both sides equally, to the desired 
thickness. The panel is then soaked in water heated to 
50° C, and then steamed. When dry, it receives a wash 
on both sides of a solution of corrosive sublimate in 
methylated spirit; it is again dried and seasoned in a warm 
air-chamber. After these operations, the panel should not 
require more than a slight rubbing with fine glass-paper, 
in order to render both surfaces plane. For panels to be 
used for oil-pictures, a priming is now applied, consisting 
of white lead, a little copal- varnish, and drying linseed- 
oil prepared by means of borate or oxalate of manganese. 
Allow this coat, which is intended to fill up the cavities 
and pores of the wood, to dry thoroughly, and then apply 
another coat in the transverse direction; subsequent coats 
should contain nothing but white lead (or other pigment) 
and the drying oil. Repeated smoothings of each coat, 
when hard, with fine pumice-powder are necessary; the 
last coat may consist of zinc-white and drying-oil. Both 
sides of the panel should be treated, as far as possible, 
alike, so that they may be equally loaded, and equally 
protected ; but the pumice-rubbings are, of course, not 
required for the back of the panel. The object of priming 
the back is twofold — the prevention of decay and of the 
attacks of insects ; and the avoidance of that gradual cur- 
vature whereby the protected front becomes convex, and 
the unprotected back concave. This change occurs 
through the slow loss of water from the back of the panel 
— a loss which is generally accompanied by a loss of some 
of the organic constituents of the wood through oxidation. 
Here it may be mentioned that the original steaming of the 
panel removes some of the extractives, and coagulates the 
albuminoids present, which are generally the first cause 



32 PREPARATION OF PANELS 

of decay. This decay is not primarily a chemical and 
spontaneous one, but is commenced by certain minute 
organisms, the growth and increase of which is, in part, 
dependent upon the presence of available albuminoids, but 
which involves also the destruction of some of the other 
extractives, and even of the ligno-cellulose itself. The 
corrosive sublimate employed helps to sterilize the wood, 
and to prevent the inroads of animal organisms. 

In order to avoid the disastrous effects of transverse 
shrinkage upon compound panels, the old painters glued 
linen cloth, or vellum, or parchment, or tinfoil to the front 
surface of the wood, and on this they spread their gesso or 
painting-ground. Gesso, made of plaster of Paris and size, 
or of whitening and size, often lost its cohesion through 
the decay of the binding material, and in consequence 
became fragile and powdery ; the panel itself decayed, and 
thus at last the linen or parchment remained as the best 
preserved element of the composite structure. Were we 
to avoid gesso and use lead-primed canvas glued to panel, 
we should really be painting upon canvas backed or pro- 
tected by wood. Panel is to be recommended for modern 
work only when a single piece of uniform and well-seasoned 
wood of sufficient size can be secured. However, an 
excellent cement for joining panels together was some- 
times used with success. It consisted of lime and cheese, 
both in fine powder, the latter having been grated, and 
then washed with water. These materials intimately 
mixed and then ground into a paste with water, yield a 
tough and adhesive cement which becomes of rocky 
hardness. 

In order to prepare a panel for tempera work, it should 
be treated in the manner above described, substituting 
for the priming with oil, white lead and copal-varnish, a 



PREPARATION OF PANELS 33 

mixture consisting partly of parchment-size, partly of 
fish-glue, and whitening. 

It is very probable that some of the hard, fine-grained 
woods of British India and of North Borneo will furnish 
excellent materials for picture-panels. At present experi- 
ments in this direction cannot be regarded as more than 
tentative and promising. 



CHAPTER IV 

CANVAS 

The usual, and probably the best fibre for the manu- 
facture of canvas for painting is unbleached flax — that is, 
linen; hemp and cotton are decidedly inferior. The 
material is woven in different ways, and with strands of 
different degrees of fineness, so as to produce cloths of 
various degrees of thickness and fineness, and having 
several kinds of texture and surface. 

The canvas is first treated with size or a solution of 
glue ; this should be as free from colour as possible : the 
addition of honey to the size is undesirable. The priming 
consists of two coats, the first containing whitening and 
size, the second lead white and linseed oil. Fuller primings 
are often given where it is not desired to allow the texture 
of the canvas to remain evident. Such primings are put 
on alternately in directions at right angles to one another, 
and are treated in the same way as the primings of panel- 
If before the last priming be dry it be dusted with zinc 
white, or if a very thin final priming of zinc white and 
drying oil (free from lead) be given, the usual discoloration 
of the canvas which occurs on keeping it, especially in the 
dark, will be avoided. But such discoloration can always 
be removed by leaving in contact with the priming a 
piece of blotting-paper saturated with a solution of 

34 



CANVAS 



35 



hydrogen peroxide : a slight warmth greatly hastens the 
bleaching process. 

Some painters in oil have employed with success a tem- 
pera-priming on their canvases. This priming may be pre- 
pared with a mixture of a strong, though elastic, size, with 
whitening. A good composition of this sort may be made 
by taking equal weights of fine whitening and of fine 
plaster of Paris, which has been slaked in and soaked with 
abundance of clean water, or of the preparation called 
satin-finish, an artificial gypsum, used by paper-makers : 
the warm size is incorporated with this mixture. When 
the priming coats are dry the surface is dressed with a 
layer of pure size, and allowed to harden thoroughly before 
the picture is begun. 

An ordinary primed canvas was examined with the 
following results. The amount of moisture present was 
5*5 per cent, of its weight, the priming 25 per cent., and 
the dry substance of the size 15. The dry fibre which 
constituted the remaining constituent would weigh, there- 
fore, about 54 parts. It was further found, with the same 
canvas, in a dry heat of 100° C. (212° F.) continued for 
twenty minutes, that a strip 20 inches long became shorter 
by a quarter of an inch, changing in colour from a creamy 
white to a pale buff. After immersion in boiling water 
for twenty minutes a piece of this canvas 20 inches square 
was found to have shrunk more than i inch in one direc- 
tion, and in the other direction rather more than half an 
inch. The piece was somewhat crinkled, and had become 
yellow in patches. 

A few remarks as to the bearing of the above observa- 
tions on some of the phenomena presented by oil-paintings 
on canvas may be here introduced. The water present in 
canvas varies with the temperature, and in consequence 



36 PRESERVATION OF CANVAS 

the dimensions of the canvas vary. As the contraction on 
drying* and the expansion on taking up moisture are not 
the same in the direction of the warp as in that of the woof, 
there is an unequal strain upon the layers of paint upon the 
surface. These may, therefore, become irregularly fissured, 
and even loosened. The importance of selecting a canvas 
so woven as to expand nearly equally in both directions is 
evident, but the maintenance of a uniform temperature, and 
of a suitable degree of moisture in the atmosphere where 
pictures are hung, is also obvious. The absorption of 
moisture by canvas occurs through the back, unless that 
be also protected by paint. With the moisture deleterious 
gases may also be absorbed, and these may easily pass 
through and affect the priming, even the picture. Canvas 
protected by panel behind, or coated at the back with a 
layer of white lead which has been ground up with starch 
paste, escapes this injury in great measure, as the sulphur- 
etted hydrogen, etc., are then intercepted. The colouring- 
matter of the fibre and size of the canvas may move towards 
the front and discolour the priming and even the picture. 
An excess of damp and a high temperature are the chief 
causes of this movement. When the first priming coat con- 
tains size, though it may adhere firmly to the sized canvas, 
it may not hold the subsequent oil-painting quite so tena- 
ciously. Canvas is liable to accidental injuries from 
mechanical causes: a double canvas mitigates the evil. The 
elasticity of the priming may not suffice, when the canvas is 
rolled up, to prevent cracking. A small addition of a non- 
drying oil, such as almond or olive oil, to the linseed oil 
used in the priming coats, proves useful, but such addition 

* Note that this contraction occurs at ordinary temperatures, 
and must be distinguished from the contraction caused by boiling 
water. 



PRESERVATION OF CANVAS 37 

should not exceed i part of non-drying oil to 20 of 
drying oil. 

There are two methods of preserving canvas from decay 
by the application of solutions to the back after the priming 
has been completed on the front. One of these solutions 
contains corrosive sublimate (mercuric chloride) dissolved 
in methylated spirit : a 5 per cent, solution is sufficiently 
strong. The other solution is made by dissolving tannin 
in methylated spirit. One or other of these solutions 
should be applied once to the back of the canvas by means 
of a broad stiff varnish-brush. When the spirit has 
evaporated, the coating of white lead ground in starch 
paste previously recommended in this chapter may be 
applied. The two solutions we have named act by coagu- 
lating some of the size in the canvas : the tannin turns it 
into leather. Corrosive sublimate prevents the develop- 
ment of mould or mildew, and is a good preservative 
against the attack of animal organisms. 

It may be observed that the employment of size in the 
first preparation of canvas constitutes an element of weak- 
ness. Many attempts have been made to substitute a less 
hygroscopic and changeable substance. A plain collodion 
containing a little ceresin (the hard paraffin from ozokerite, 
or earth-wax) has been used for the purpose in question. 
It is, however, very difficult to secure the adhesion to the 
canvas of the film left behind when the collodion dries. 
I have found that oil-paintings executed upon collodion- 
ized canvas cannot be rolled up without damage. It 
would probably be found that the formation of a viscose 
film (see the account previously given of paper-sizing) 
would prove a good substitute for ordinary size in the 
first treatment of canvas. 

^ The majority of pictures nowadays are painted on 



38 PRESERVATION OF CANVAS 

canvas, though it must be admitted that, especially in 
respect of mechanical and chemical durability, it is a very 
unsatisfactory material. Its light weight, its cheapness, 
and the possibility of rolling up pictures painted upon it, 
offer some advantages, no doubt, although the last charac- 
teristic is of questionable value. On the whole, the draw- 
backs to the use of canvas preponderate over its merits. 
In this connexion special reference should be made to the 
very marked alteration in dimension caused by damp (see 
p. 36). This persistent working or movement of the ground 
can be checked in the case of large collections gathered in 
galleries duly equipped with the latest technical appliances 
for the careful regulation of humidity and temperature. 
But the case is different in private rooms where the move- 
ment in question is practically unavoidable, and inevitably 
leads to cracking in the course of time. This change is 
still further promoted by the action of the oxygen in the 
atmosphere, which attacks the painting both back and 
front, and, by producing a gradual alteration in the binding 
material, brings about a corresponding deterioration in 
the adhesion and cohesion of the pigments. Moreover, 
from the same cause, the linen or hemp fibre itself 
becomes after a time so brittle that it is scarcely capable 
of affording adequate support to the painted layer. When 
it reaches such a state a picture must be ' relined ' — i.e.^ 
stretched on a fresh canvas. The painting itself may 
thus prove more durable than the material base which 
was designed to secure its durability. 

^ The stability of pictures painted on canvas is en- 
hanced if the back be protected by a metallic coating, so 
as to protect it in a measure, on that side at least, from the 
inroads of oxygen. The simplest way to secure this result 
is by coating the back with tinfoil, using to fix the metal 



PRESERVATION OF CANVAS 39 

in position a strong solution of shellac* in spirits of wine. 
In order to guard against the penetration of oxygen through 
the accidental holes occurring in the tinfoil, a second 
sheet of this metal may be added when the shellac solu- 
tion has become dry. This treatment may be applied 
generally to pictures painted on canvas, and virtually 
doubles their span of life. 

^ But protection from mechanical injury is not ensured 
by a thin coating of tinfoil. If that further protection be 
desired the back of the painting may be lined with sheet 
metal. According to the size of the picture, sheet copper 
or brass, or even sheet iron coated with tin or zinc, may 
be employed. Paintings executed on canvas may be 
fastened to the sheet of metal by the shellac "'^ cement 
before named or with thick amber varnish. Thus the back 
becomes protected both chemically and mechanically by 
the same contrivance, and a high degree of durability is 
thus assured for the picture. 

H When it is a question of producing new pictures the 
painting may be executed directly on metal. Such a 
procedure applied to sheet copper was frequent with 
Dutch miniaturists : the flawless condition of their works 
justifies this method from the present point of view. Yet, 
as this use of copper involves some risk that its green 
and blue oxidation-products may give rise to discoloration, 
a more appropriate painting-ground is offered by sheet 
aluminium, which yields only colourless compounds. 
Moreover, when aluminium is exposed to the atmosphere 
there is formed on the surface a transparent and imper- 
ceptible film of oxide which retains oil-colours very firmly. 
Even on unprepared surfaces of aluminium it is possible 
to paint very easily, for the metal possesses a peculiar 

* Perhaps marouflage is preferable (see p. 26). 



40 LINOLEUM 

' tooth ' in relation to the paint so that one can readily lay 
on successive coats of paint, stroke by stroke. Some 
years ago I covered a piece of sheet aluminium with a 
coating of oil-paint and exposed it in the laboratory to all 
the accidents of the place. The paint remains sound to 
this day and shows no tendency to crack or peel. A 
sketch executed on strong sheet aluminium stands in a 
greenhouse, where it receives all available sunshine and is 
exposed to great variations of temperature : after exposure 
during six months of spring and summer it showed no 
signs of change for the worse. There is therefore good 
reason for contending that in sheet aluminium we 
possess an ideal painting -ground, especially for work 
in oils. 

H Another material which seems to lend itself particu- 
larly to decorative and monumental painting is linoleum. 
This consists of a very strong fabric coated with a thick 
layer of oxidized linseed oil mixed with cork-raspings and 
other materials. It thus bears some resemblance to canvas 
which has been primed for the reception of oil colours, but 
differs in its greater solidity and in the elastic substances 
which it contains. The fact that the body of linoleum 
consists mainly of the same substance that forms the bind- 
ing material in ordinary oil-painting sufficiently guarantees 
permanent union between picture and ground. From 
another point of view the massive nature of the material 
almost completely obviates the risk of mechanical injury, 
and affords at the same time complete protection from the 
attacks of air and damp at the back. If the brown colour 
be not an objection, the surface can be used just as it is 
as a painting-ground ; in this case the various rough and 
smooth sorts of linoleum provide an agreeable choice of 
surfaces from the artistic standpoint. But it will be 



LINOLEUM 41 

found better to lay on a thin coat of white oil-paint, 
especially in the case of pictures intended to present a 
bright general tone. Or a white pigment may be incor- 
porated with the mass of the linoleum itself and so the 
brilliancy of the applied colours may be enhanced. As 
linoleum is manufactured several yards wide, it is possible 
to paint very large pictures on a single piece, so that this 
material seems more suitable for monumental or large 
decorative works. It should not be fixed directly to the 
wall, but attached to a metal framework covered with 
galvanized iron wire netting and erected at a small dis- 
tance from the wall ; the danger of injury from damp or 
fracture is thus avoided. 

With reference to the two materials, linoleum and sheet 
aluminium, recommended in the preceding paragraphs for 
use as painting-grounds, a few further observations may 
be advisable. The variety of linoleum in which the 
canvas-backing is omitted — solid linoleum — is not suit- 
able for the purpose under discussion, for there is some 
risk when large pieces are used of its sagging, and even 
splitting, after the lapse of some time. And the experi- 
ence of coach-builders is not altogether in favour of alu- 
minium for the reception of a coating of oil-paint. In 
some instances, at all events, there are signs of the dis- 
integration of the metal and consequent cracking of the 
superimposed layers of pigment. Possibly these draw- 
backs may not occur where the painted surfaces are not 
exposed to the external atmosphere. And it must be 
remembered that the sheet aluminium of commerce varies 
somewhat in its composition and properties. 

' Willesden canvas ' appears to resist the attack of 
moisture and of animal organisms: the copper-compounds 
which it contains do not interfere with its use as a painting- 



42 'WILLESDEN CANVAS' 

ground, but the absence of soluble salts (chiefly sulphates) 
from it should be ascertained. This test is easily made by 
soaking a piece of the canvas weighing 50 grains in dis- 
tilled water overnight, pouring off the clear liquid next 
morning, heating it to boiling, and adding a few drops of 
barium chloride solution and of dilute nitric acid. If a 
distinct precipitate be formed the canvas cannot be em- 
ployed safely, but a mere cloudiness may be disregarded. 
It is just as well to test the watery extract for free acid by 
means of litmus paper, because an attempt has been made 
to remove the green colour of Willesden canvas by a bath 
of dilute sulphuric acid, the presence of which is, on all 
accounts, to be avoided. ' Willesden paper ' possesses 
properties similar to those of Willesden canvas, and may 
sometimes be found serviceable for work in oil-colours. 



PART II 
VEHICLES AND VARNISHES 

Chapter V.— Oils. Chapter VI. — Resins, Waxes, Paraffin-Waxes. 
Chapter VII.— Yolk and White of Egg, Size, Glue. Chapter VIII. 
—Gums, Glycerin, Honey. Chapter IX.— Water- Glass, Lime- 
and Baryta-Water. Chapter X. — Solvents and Diluents. Chap- 
ter XI.— Siccatives and Dryers. Chapter XII. — Varnishes and 
Oleo-Resinous Vehicles. 



CHAPTER V 

OILS 

The common usage of the term ' oil ' is wider and less 
definite than that sanctioned by chemists. We must 
exclude from the category of true oils petroleum and 
the liquid paraffins, spirit of turpentine and the volatile 
essences of plants, the hydrocarbons of coal naphtha, as 
well as a number of other liquids which present certain 
superficial resemblances to the oils proper. Fats, how- 
ever, belong to the same group, their solidity at ordinary 
temperatures being, so to speak, an accidental rather than 
an essential diiTerence. 

The true oils are often called fixed oils, for they cannot 
be boiled and distilled without change, thus differing from 
really volatile liquids. They are glycevides — that is, com- 
pounds from which glycerin, on the one hand, and fatty 
acids, on the other, are obtainable. These glycerides are 
named after the fatty acids which they yield. Thus olein 
is the glyceride of oleic acid, linolein the glyceride of lino- 
leic acid. In reality three kinds or varieties of glycerides 
of each fatty acid are possible, but the oils used by painters 
consist almost entirely of one of these kinds. The forma- 
tion of one of these glycerides may be expressed in words 
thus : One molecule of glycerin, reacting with three mole- 
cules of a fatty acid, yields one molecule of the glyceride 

45 



46 DRYING OILS 

in question and three molecules of water. Conversely, 
under other conditions, one molecule of a glyceride, re- 
acting with three molecules of water, produces one mole- 
cule of glycerin and three molecules of fatty acid. If, in 
this last reaction, we substitute for the water three mole- 
cules of an alkali, such as potash, we obtain glycerin as 
before ; but, in lieu of the free fatty acid, we find that an 
alkaline salt of the fatty acid has been formed — such salt 
is a soap. Alkaline soaps, namely, those of potash, soda, 
ammonia, are soluble in water, which fatty acids — at any 
rate, those with which we are here concerned — are not. 
There are, however, other soaps which are insoluble in 
water, namely, the lime, lead, copper, and many similar 
metallic salts of fatty acids. 

Oils, though insoluble in water, are easily soluble in 
spirit of turpentine and other volatile plant essences ; 
in benzene, chloroform, and liquid paraffins ; they are, 
in fact, miscible in all proportions with these liquids. 
There are other liquids in which the oils are less soluble, 
such as alcohol, acetone, and glacial acetic acid. 

Oils are divisible into two classes, one of which includes 
those which dry up and harden, forming a kind of elastic 
varnish, by exposure to the air. The oils of the other 
class do not harden, but become sticky, and rancid in 
smell ; these oils, however, if submitted to the tempera- 
ture of boiling water for some time, do in some instances 
become dry and hard, but the varnish they yield under 
these circumstances is dark in colour and brittle ; it has 
been suggested that some of these should be grouped to- 
gether in a third class as * semi-drying' oils. The painter's 
concern is almost exclusively confined to the oils of the 
first group, generally known as drying oils. To the most 
important of these attention will be directed presently, 



LINSEED OIL 47 

but the general methods of extracting them first demand 
a few words of explanation. There are two different pro- 
cesses in use. In one of these, which has been practised 
widely from very early times, the oil is obtained by 
pressure ; in the other process, invented some seventy 
years ago, the oil is extracted by means of an appropriate 
solvent. We may dismiss this latter process almost 
summarily, for the product which it yields, though much 
greater in quantity, is decidedly inferior to that obtained 
by pressure. It is less fluid, and contains a larger propor- 
tion of solid fats. The solvent commonly employed to 
dissolve out the oil from oil-yielding materials is carbon 
bisulphide (CSg), a compound of carbon and sulphur, 
which may be prepared cheaply by passing the vapour of 
sulphur through red-hot charcoal. Of the pressure-process 
for obtaining fixed oils there are two modifications. In 
the more usually adopted of these, the oily seed or other 
material is first heated, and then pressed while still hot ; 
in the other modification the pressure is applied to the 
cold seed, etc. Heat and pressure give a more abundant 
yield of oil, but the product is less pure and less well fitted 
for use in painting. The bulk of the oils of commerce are 
thus obtained. Cold-pressed oils remain clear in cold 
weather, are more fluid than hot-pressed oils, and con- 
tain a smaller proportion of solid fats and of free fatty 
acids. 

The most important drying oils are those of linseed, 
poppy-seed, and walnut kernels; others are obtained 
from niger-seed, sunflower-seed, and hemp-seed. The 
first place is due to linseed oil. 

Linseed oil is obtained from the seed of the common 
cultivated flax (Linum iisitatissimimi). Linseed varies in 
size and colour. The usual colours are a purplish-brown 



48 LINSEED OIL 

and a reddish- brown, but there is a nearly white sort — a 
mere sport or variety — which may be said to be straw- 
coloured. It is grown along with the brown variety in 
some parts of the North- West Provinces of India, par 
ticularly in Nagpur, but no pains are taken to keep the 
strain pure. Through the kind offices of the Director of 
the Royal Gardens, Kew, the Government of India were 
good enough to obtain a specially pure sample of some 
hundredweights of white Nagpur linseed, and to place it 
at my disposal. Attempts to grow it for seed in this 
country and in Belgium failed, but a large quantity of 
oil was expressed for trial and analysis. Messrs. Bell 
and Co., of 225, Oxford Street, obtained several gallons 
of oil by cold-pressure ; many artists have expressed 
their approval of the product. One advantage of this 
white seed is the ease with which the purity of a sample 
may be recognised by the eye, any accompanying weed- 
seeds differing widely in colour from the white linseed. 
The skin of the seed is, moreover, thin, the cold-drawn 
oil is nearly colourless, and the seed is particularly rich 
in oil, containing no less than 45 per cent, of its weight, 
although, of course, much less than this proportion is 
obtainable by cold-pressure. In a hand-press about 
25 per cent, was the average yield. Of the common or 
brown linseed our chief supplies come from Russia and 
India. The Russian seed is generally finer than the 
East Indian ; it is, moreover, imported in a less mixed 
and impure condition. By screening, the greater part of 
the impurities are or may be removed, but it is sold on a 
basis of 4 per cent, impurity. The impurities consist of 
dirt, other oil-seeds, such as mustard, rape, and gold of 
pleasure, and non-oily weed-seeds. The presence of the 
last-named, though it reduces the yield, is not otherwise 



LINSEED OIL 49 

objectionable,* but the same remark does not apply to 
the foreign oil-seeds. Most of these contain non-drying 
oils, which mingle with the linseed oil when the sample 
is pressed and reduce its siccative character. Much 
linseed now comes from the Argentine, Canada, and the 
United States, as well as from India and Russia. 

The percentage of oil in linseed varies between 28 and 
45 : by cold-pressure 20 per cent, is the average yield ; by 
hot-pressure, 27 per cent. ; by extraction with carbon 
disulphide, 33 per cent The linseed oil in common use 
by artists is hot-pressed oil, and is very rarely, if ever, 
obtained from absolutely pure seed. The seed should be 
kept three months before it is pressed. The expressed 
oil should be exposed to light in covered glass vessels or 
tanks, and kept at a temperature of 212** F. for some 
time. It thus loses colour and becomes clear, a slimy 
deposit containing mucilage, albuminoid matter, and 
traces of a cyanogenetic glucoside, being formed. When 
thus bleached and clarified, the oil should be preserved 
in corked bottles filled quite full ; the longer it is kept, the 
better it becomes for painting, provided the access of air 
is prevented. The specific gravity of good linseed oil 
varies very little. At 60° F. (15-6° C.) it is -935 ; a bottle 
which will hold 1,000 grains of water at this temperature 
will therefore hold but 935 grains of hnseed oil. It 
expands considerably with heat, its specific gravity at 
50° C. being -913 only. One part of linseed oil requires 
36 parts of cold absolute alcohol for solution, but only 
4 parts of boiling alcohol. It may be purified by solution 
in boiling alcohol or in petroleum ether. Other methods of 
purification are generally employed. Amongst these may 

* Occasionally these weed-seeds give up, under pressure, certain 
matters which deepen the colour of the expressed oil somewhat. 

4 



50 LINSEED OIL 

be named the following : Filtration through felt or carded 
cotton and charcoal, and then through pyrolusite ; con- 
tact for some weeks with 3 per cent, of a mixture of 
equal parts of kaolin and aluminium hydrate, both these 
compounds having been previously dried at about 50° C; 
agitation with a solution of common salt, followed by 
washing wth water, and drying by a heat of 220° F. ; 
treatment with one four-hundredth part of oil of vitriol, 
addition of hot water, washing, and drying. Various 
other processes and reagents have been employed for 
purifying and bleaching linseed oil. Aqueous solutions 
of sulphurous acid, green vitriol, potassium permangan- 
ate, potassium bichromate, and peroxide of hydrogen 
may be included in this list. The addition of i per cent. 
of oil of turpentine to the oil, and then passing a mixture 
of air and steam through it, has also been tried. What- 
ever process be adopted, no acid, saline matter, or 
moisture must be left in the oil. The general and usual 
result of all the very different kinds of treatment to 
which linseed oil is subjected, in the above-named and in 
many other processes, seems to be the more or less com- 
plete removal of impurities. The effect on the properties 
of the purified oil is chiefly seen in its greatly increased 
rate of absorbing oxygen and consequent hardening. 

The chemical composition of linseed oil may now 
engage our attention. Its ultimate analysis shows it to 
vary according to the method of extraction adopted, cold- 
pressed oil containing about 78 per cent, of carbon, 1 1 per 
cent, of hydrogen, and 1 1 per cent, of oxygen ; while the 
hot-pressed oil contains nearly 3 per cent, less carbon, 
and nearly 3 per cent, more oxygen — linseed oil, extracted 
by carbon disulphide, is still poorer in carbon, and richer 
in oxygen. It appears that linseed oil consists chiefly of 



LINSEED OIL 51 

three glycerides, called, respectively, linolein, linolenin, 
and olein. A small, but variable, amount of free fatty 
acids, such as palmitic and arachidic, is also present. 
The empirical formulae of the three fatty acids of the 
above-named glycerides are, respectively : 

Linolenic Acid - - CJ8H3QO2. 
Linoleic - - - - CigHggOa. 
Oleic - - - - CigHgjOg. 

Linolein, which is present in linseed oil to the extent of 
about 20 per cent., is the glyceride of linoleic acid, and 
has the formula (C^^2.fi)^,C^ll^jO^ ; or, as it may be 
written, 03115(0, C^gHg^Oyg. The relation of this glycer- 
ide to glycerin may be seen when the latter body is ex- 
pressed by the formula, C3H5(OH)3. It is probable that 
the other main constituent of the oil — linolenin — is a 
similarly constituted glyceride, and that it closely resem- 
bles linolein in physical and chemical properties. When 
100 parts of linseed oil are saponified by an alkali, they 
yield from 9-4 to 10 parts of glycerin. 

The most important chemical property of linseed oil, 
from a painter's standpoint, is its behaviour with oxygen. 
Under certain circumstances, it absorbs oxygen to the 
extent of 13 or even 14 per cent, of its weight, becoming 
converted into a mixture of substances for which it is con- 
venient to retain the old name linoxine. Linoxine is solid, 
and not liquid ; it is far less soluble than linseed oil in any 
solvent, and in many liquids it is insoluble. Linoxine 
is, moreover, denser than the original oil ; 100 grains of 
linseed oil produce about 109 or no grains of linoxine. 
Notwithstanding the greater density of linoxine, when 
compared with the original oil, its formation is attended by 
a considerable expansion. In consequence, a layer of raw 



52 LINSEED OIL 

linseed oil spread upon glass becomes wrinkled during the 
drying and oxidizing process. During the oxidation of 
linseed oil, the small quantity of olein it contains remains 
unoxidized — its presence confers elasticity upon the pro- 
duct. 

H The incidents associated with the hardening or solidi- 
fying of drying oils have always been an attractive study, 
but it is only through the chemico-physical researches of 
recent years that their true nature has been made clear. 
The most important points will now be briefly explained. 
This hardening depends, as before stated, on a process of 
oxidation — that is, on the absorption of free oxygen from 
the atmosphere. During this process carbon dioxide and 
other volatile organic compounds are formed and given 
off, while simultaneously there are produced solid, non- 
volatile bodies which constitute the dried and hardened 
oil. These solids then, in their turn, by a further and 
very slow oxidation, yield other volatile products. While 
in the first stage, the gain in weight of the oil, due to the 
absorption of oxygen, far more than compensates for the 
loss which arises from the escape of volatile matters, in 
the second stage there is a distinct diminution in bulk and 
in weight, while the residue acquires a deepening brown 
hue. This last phenomenon, however, does not seem to 
be inevitable, for it occurs when light is excluded ; and 
this yellowing or embrowning of the hardened oil may 
often be remedied by subsequent exposure to light, 
although it does occur in many pictures which hang on 
well-lighted walls. As this change does not take place 
always, it seems reasonable to conclude that, putting 
aside discoloration through the deposition of dirt and 
sooty matters, it must arise by an alteration in something 
present which is not oil. Indeed, it seems to be trace- 



LINSEED OIL 53 

able to the presence of lead introduced into the oil used 
as a siccative or dryer. As equally efficient dryers may 
be prepared without the employment of lead compounds, 
it seems desirable that these should be rejected. 

U If a thin layer of linseed oil be put into a bottle full 
of air and provided with a contrivance for observing the 
absorption of the oxygen, it will be seen that at first the 
oxidation proceeds very slowly — this is Period I. The 
absorption then becomes more and more rapid till it 
reaches a maximum — this constitutes Period 11. Once 
more the absorption becomes slow — this is Period III. 
It is only during this last period that the oil loses its 
fluidity, becoming first viscous and finally solid. Oil 
examined at the close of the second period or stage dries 
quickly, and is often called varnish. 

%_ The processes just described, if carried out in the 
dark, occupy some weeks, but they may be hastened by 
means of several different agents. For instance, by heat — 
that is, by raising the temperature. It is a general law that 
the rate of chemical action increases proportionately with 
rise in temperature. Thus the higher the temperature at 
which the linseed oil absorbs oxygen, the more ra,pid 
does the action become. It is on this fact that the very 
old process of varnish-making by boiling raw linseed oil 
rests. The oil, heated in open vessels up to a fairly high 
temperature (200° C. or more) absorbs oxygen rapidly, 
while at the same time, principally through the overheating 
of the sides of the vessels used, some brown decomposition 
products, which give the varnish a dark colour, are formed. 
If the heating be stopped when the oil is in its second 
stage of oxidation, a product is obtained which, though 
still fluid, has acquired the property of absorbing with 
great rapidity the small amount of oxygen still needed to 



54 LINSEED OIL 

render it solid. Oil thus treated dries, therefore, much 
more quickly than raw oil, and is used when quick drying 
is of importance ; it is known as linseed oil varnish. 
However, along with the advantage of quick drying, its 
dark colour constitutes a drawback. But this discolora- 
tion, being due to excessive and unequal heating, can be 
avoided by conducting the operation of limited oxidizing 
at a moderately high temperature (say ioo° to 150° C). 
It may, too, be hastened by passing a stream of air 
through the heated oil. In this way, not only is discolora- 
tion avoided, but the oil is actually bleached, and a nearly 
colourless varnish produced. If the treatment be stopped 
at the right moment, a sufficiently fluid varnish is ob- 
tained, while if the process is carried farther, viscous and 
almost solid products are formed. Naturally this mode 
of preparing the varnish takes more time, owing to the 
lower temperature employed, than the old boiling process, 
but the product is much better. 

IT The second agent which may be employed to hasten 
the oxidation of oil is light, which acts energetically. On 
this fact depends the process of transforming linseed oil 
into varnish by exposing it to sunshine in shallow vessels, 
so as to facilitate the access of light, care being taken to 
exclude dust, while the oil is occasionally stirred in order 
to prevent a skin being formed on the surface through a 
superficial oxidation. If this skin be produced, it hinders 
the access of oxygen to the oil beneath, while the product 
is not homogeneous. It is on this action of light that a 
common practice of artists is based, the placing a picture 
in the sun that it may dry quickly. The converse prac- 
tice, however, of keeping paintings soft and moist during 
the time when the artist is not working upon them, by 
excluding light from them, is less known. The best 



LINSEED OIL 55 

means of securing this object consists in arranging a 
sheet of aluminium in front of the picture so as not to 
touch the surface ; it is light in weight, and rigid. 

U A third agency which may be used to hasten the oxi- 
dation of a drying oil is to be found in the presence of one 
or other of a group of substances, the mere presence of 
which when the oil is still in its first stage may reduce the 
time required to reach a condition of solidity from days 
to hours. Some compounds of lead and manganese are 
the best known of these active materials. Innumerable 
old recipes for varnish boiling and for preparing varnish 
in the cold are based on the solution in oil, in one way or 
another, of certain compounds of the metals just named. 
Since it is only within comparatively recent times that the 
conditions, under which the oxidation of drying oils pro- 
ceeds, have been clearly understood, it is to be expected that 
these old recipes should prescribe a number of superfluous 
and, indeed, actually injurious operations. In order to 
obtain a quickly drying oil it is requisite merely to dissolve 
a suitable and generally a very small quantity of one of 
these ' accelerators ' in the oil, and to carry the oxidation 
process no farther than to the second stage or period. 
Lead, which has been longest known as a ' dryer,' is best 
used in the form of its linoleate or resinate, as these com- 
pounds dissolve in oil, especially when warmed. Strong 
solutions of this kind, generally dark in colour, are put on 
the market as siccatives, and added by artists to their 
oil-paints on the palette in a haphazard manner. Such is 
an injudicious procedure and may have an injurious effect 
on the durability of the picture. For when thus added 
the dryer is more or less unevenly distributed, not only 
throughout the picture as a whole, but even in different 
portions of the same paint. Thus there ensues uneven 



56 LINSEED OIL 

drying and the formation of cracks is promoted. It is 
better to add the proper quantity of the dryer to the 
paints in the first instance. 

During recent years many improved methods of treating 
raw linseed oil have been devised. The ' boiling ' has 
been carried out in aluminium vessels in lieu of those of 
iron, which become much corroded through the action of 
the free acids of the oil upon this metal. The iron com- 
pounds thus formed are undesirable ingredients of the 
boiled oil. Then, again, superheated steam has taken 
the place of direct fire-heat in treating the oil, which is 
mechanically stirred while a current of oxygen or of air 
is at the same time sent through the liquid. In yet an 
other process, the raw oil in the form of spray and heated 
is brought into intimate contact with a stream of heated 
air. There exists also an improved method of preparing 
a drying oil by the agency of light. As it has been found 
that sunlight acts mainly in virtue of its ultra-violet or 
actinic rays, an artificial light, singularly rich in such 
rays, has been substituted for the light of the sun. This 
is found in the mercury lamp, in which an electric spark, 
passing between two mercury poles enclosed in a quartz- 
glass tube, originates a peculiar light of high activity. A 
battery of such lamps is so arranged that their radiation 
impinges upon the oil, which is at the same time kept at 
a temperature of 80° C, while a finely divided stream of 
oxygen gas is forced through it. The pale, quickly drying 
oil thus produced is said to possess the property of drying 
uniformly throughout without the production of a skin on 
the surface. 

The changes which occur during the oxidation of 
linseed oil, as described in the preceding paragraphs, 
are, as will have been seen, complex ; but there is 
some formic acid formed, so that the product is sour — 



LINSEED OIL 



57 



carbonic acid gas and water are also produced. It 
has been shown that there are many ways of bringing 
about this oxidation. A very common one is to heat 
the oil to a temperature of at least ioo° C, and to blow 
air through it, or air containing ozone. Many sub- 
stances favour the absorption of oxygen by linseed oil 
under the above conditions. Amongst these may be 
named manganese dioxide, borate, oxalate, resinate, or 
linoleate ; cobalt resinate ; red-lead, litharge, or lead ace- 
tate ; green vitriol, iron in the presence of water, etc. It 
is better to use one of the manganese compounds, and an 
excellent result is obtained with the borate of this metal. 
On the small scale, the operation may be thus carried out : 
Tie up in a small piece of muslin 20 grains of dry and 
powdered manganese borate. Suspend the bag in a glass 
quart flask, into which a pint of linseed oil has been 
placed, so that the bag is just covered by the oil ; lightly 
plug the mouth of the flask with some carded cotton. 
Stand the flask in a warm place, where the temperature 
does not fall below 40° C, nor rise above 100° C. In a 
fortnight's time, the oil will have become strongly sicca- 
tive, so that when it is spread in a thin layer on glass, or 
paper, it will dry up to a tough varnish within twenty- 
four hours. If the oil and manganese borate be main- 
tained, by means of a water-bath, at a temperature of 
100° C, the change will occupy less time, and the product 
will be just as good ; but it is not advisable to hoil the oil 
with the borate, although the change may be thus eft'^ected 
in less than an hour. The oxidation may be further 
hastened by occasionally blowing a little air into the oil 
through a glass tube kept permanently in the flask. When 
the rapid-drying quality of the oil has been proved, by 
experiments made with a drop or two Vv^ithdrawn for that 
purpose, the flask is allowed to get cold, and the oil 



58 SICCATIVE LINSEED OIL 

poured into a corked glass bottle, so as to fill it. In the 
course of the next few weeks, a slight deposit will be 
formed in the bottle ; when this has occurred, the clear oil 
should be poured off into other bottles, and preserved for 
use. According to the purpose for which the prepared oil 
is to be afterwards used, the treatment with the borate must 
be more or less prolonged ; but care should be taken not to 
carry it so far that the oil becomes ropy or viscous, unless 
it is intended to make linseed oil varnish. In the subse- 
quent chapters of this book we shall often refer to this 
siccative linseed oil as ' manganese oil.' To the above 
directions for preparing this oil may be added the remark 
that if the operations be conducted in a strong light, the 
oil will be bleached, as well as rendered highly siccative. 
No satisfactory explanation of the action of the manganese 
borate (and of many other substances used for the same 
purpose) has been offered. But it seems probable that 
the absorption of oxygen by the oil is favoured by the 
removal of certain impurities, and this the borate of 
manganese may effect : it has been suggested that the 
action is in part catalytic. 

The increasing specific gravity of the ' manganese oil,' 
as the process is prolonged, may be used as an indication 
of the point at which the heating may be discontinued. 
When the oil has acquired a specific gravity of -945, it is 
generally sufficiently siccative for grinding with non- 
drying pigments, and as an addition to certain varnishes. 
For these purposes it may even attain a specific gravity 
of -96 ; but when it shows '99, or '995, it constitutes a 
thick varnish, which needs dilution with a suitable 
solvent. It may be well to remark here that the various 
processes for rendering linseed oil more rapidly- drying 
may be regarded as resulting in two actions, partly con- 



TESTING LINSEED OIL 59 

secutive, partly simultaneous. The first action, if it 
could, or did, occur alone, would yield a purified oil apt 
to dry quickly, but very slightly altered in composition ; 
the second action is more profound, and gives rise to a 
thickened, denser product, in which the drying process 
has already commenced. In practice, the first action 
occurs almost, but not quite, uncomplicated with the 
second, when linseed oil is warmed with borate of man- 
ganese in a vessel to which atmospheric air has very 
limited access ; the second action, which is of necessity 
associated with the first, takes place when a stream of 
air is blown through warm linseed oil, even in the absence 
of manganese borate, but far more quickly in its presence. 

The superiority of the highly siccative oils prepared 
with borate of manganese (or the oxalate, resinate, or 
linoleate) over those in the manufacture of which lead 
compounds are used, is so decided that all description of 
the older and less satisfactory methods will be omitted. 
But there are two other ways of rendering linseed oil 
more siccative, which deserve a passing notice. Into a 
clear-glass quart-bottle an ounce of distilled water and 
an ounce of clean iron brads are first placed, and then 
one pint of raw linseed oil, agitation being avoided. The 
next day, the bottle, placed in as strong a light as possible, 
is to be shaken frequently, the shaking being repeated 
every day, until a drop of the oil, when tested, shows a 
sufficient degree of drying character. Finally, the liquid 
part of the mixture in the bottle is poured into a separating- 
funnel, and the aqueous part allowed to run away. The 
oil may require drying and filtration. In another similar 
process green vitriol is substituted for the metallic iron, 
the other directions being identical. 

The most important property of linseed oil, and some 



6o TESTING LINSEED OIL 

methods for the further development of this property 
having been discussed, we may now describe the remain- 
ing characters of this oil. The cold-pressed oil is very 
pale straw-coloured, or pale yellow, with occasionally a 
faint greenish hue ; the hot-pressed oil is a darker yellow 
or brown. The cold-pressed oil, when considerably 
cooled, remains clear long after the hot-pressed oil has 
become turbid. The fluidity of the oil is less than that 
of water in the ratio of i : lo. The hot-pressed oil has a 
much stronger taste and odour than the cold-pressed oil. 

The adulteration of linseed oil with other oils may be 
recognised with more or less precision by means of 
several different tests. Most of these tests (oil of vitriol 
test, nitric acid test, etc.) produce reactions in which the 
oil and the acid acquire varied colours characteristic of 
different oils. These tests must be applied under exactly 
similar conditions of temperature, agitation, lapse of time, 
strength of acid, etc. ; and even then, unless the experi- 
menter is well-versed in the work, the indications obtained 
are sometimes perplexing and difficult to interpret. The 
amount of iodine absorbed by a given weight of linseed 
oil is also a measure of its drying power as shown in its 
capacity for absorbing oxygen. This 'iodine-value,' as 
it is called, is the amount of iodine absorbed from 
chloride of iodine in the presence of glacial acetic acid, 
by loo grammes of oil. The iodine-value for linseed oil 
is somewhere near 200; the figures for walnut oil and 
poppy oil are always lower, while the semi-drying and 
the non-drying oils may not show half this value, and 
these are the oils likely to be used as adulterants. But 
such quantitative determinations can be properly per- 
formed only_ by the skilled chemist. There is another 
test known as Valenta's acetic acid test, which has been 



POPPY OIL 6i 

used for the detection of non-drying oils in linseed oil. 
It is based upon the less solubility of the former oils in 
glacial acetic acid. It is, however, not easy to secure 
constant results with this test. Determinations of 
volatile matters, of unsaponifiable substances, and of 
insoluble bromine derivatives, afford valuable indications 
as to the purity of samples of this oil. 

The specific gravity of linseed oil also affords a valuable 
means of testing its purity. At 15*6° C. (60° F.) it is 
denser than most other vegetable oils : 



Name of Oil Spec. Grav. 


Name of Oil Spec. Gr 


Linseed - - -935 


Poppy-seed - - "926 


Gold-of- Pleasure- -931 


Sunflower-seed - '925 


Hemp-seed - - -930 


♦Black Mustard-seed- -921 


Cotton-seed- - -930 


♦Ground-nut - - "918 


Walnut - - -927 


♦Colza-seed - - -914 



The four oils marked with an asterisk are practically non-drying. 

Poppy Oil. — This oil is obtained from the seed of the 
opium-poppy, Papaver somnifenmi. It is of a very pale 
straw-colour, often almost colourless, and is nearly free 
from taste and smell. By filtration through hot animal 
charcoal it may be completely decolourized. If the fluidity 
of water be represented by 1,000, that of poppy oil at 
15-6° C. is 74. Its specific gravity at the same tempera- 
ture is -926. Its chemical composition is near that of lin- 
seed oil ; it contains the same three glycerides, but in 
different proportions, for it is mainly made up of linolein 
and olein. The large quantity present of olein causes 
poppy oil to be a less rapidly drying oil than linseed. 
Wolffen, in 1640, stated that poppy oil dries thvoughout in 
four or five days, while linseed oil forms a pellicle upon the 
surface. Joseph Petitot, writing from Geneva under date 
January 14, 1644, stated that umber is a siccative for 



62 NUT OIL 

poppy oil. Poppy oil was introduced into painting in the 
beginning of the seventeenth century, after linseed and nut 
oil. Later on in the same century the Dutch painters ac- 
quired greater confidence in this more slowly drying oil, 
employing it not only in the painting process, but also for 
grinding their pigments, especially whites, blues, and pale 
tints. 

Nut Oil. — This oil is obtained from the kernels of the 
common walnut, Juglans vegia. Leonardo da Vinci directs 
it to be made from the peeled kernels in order to avoid the 
chance of darkening its colour, and also causing the subse- 
quent alteration of the tone of the pictures painted with it. 
The kernels were to be soaked in water first, before being 
peeled and pressed. The introduction of nut oil into 
painting followed that of linseed oil, and preceded that of 
poppy. Cold-pressed nut oil is much paler in colour, and 
has much less taste and smell than the hot-pressed oil ; it 
also differs in composition much in the same way that cold- 
pressed differs from hot-pressed linseed oil. The con- 
stituent glycerides of nut oil are the same in kind as those 
of linseed oil, but a larger proportion of linolein is present. 
Nut oil closely resembles linseed oil in its physical charac- 
ters ; its specific gravity, '929, is intermediate between 
that of linseed and poppy oil : cold pressed oil from the 
Black walnut {Juglans nigra) has the specific gravity '922, 
and is quite as good for painting purposes as oil from the 
common walnut. Besides the three drying oils already 
described we may name that expressed from niger-seed, 
Guizotea oleifera. It is occasionally employed in grinding 
artists' colours as a substitute for linseed and poppy oil. 
Tea-seed and camellia-seed oils, and the oils extracted in 
Japan from the seeds of Perilla ocimoides and from the 
kernels of Torreya nucifera^ are not of sufficient importance 



ACTION OF PIGMENTS ON OILS 63 

to demand description. There is, however, one remark- 
able drying oil of recent introduction which ought to be 
named here. This is Chinese Wood oil or Tung oil ob- 
tained from the seeds of A leurites cordata. It is distinguished 
from the oils we have been discussing by the change 
which it undergoes when heated to about 282° to 285° C. 
After having been maintained at this temperature for a 
few minutes the oil becomes a gelatinous mass, firm and 
free from stickiness. Tung oil is heavier than any of the 
oils hitherto described. It is probable that it may find 
certain applications in artistic painting, for it has been 
shown to yield a durable film when oxidized. 

A few observations may now be offered as to (i) the 
action of certain pigments on oils; (2) the different amounts 
of oil needed for grinding with different pigments. 

I. Action of Pigments on Oils. — The most common action 
is a physical one, in which the opacity of a pigment is 
gradually lessened in course of time by the more complete 
interpenetration of the oil between the particles. Thus 
yellow ochre and raw sienna, for example, darken in colour 
because they become more translucent, just as a piece of 
oiled cream-laid paper is darker and yellower than the 
same paper when dry. The light which falls upon it 
plunges into it more deeply, and on reflection is more 
highly coloured. In the case of such pigments as we 
have named, and several others, another cause is at work 
darkening and modifying the colour : this is the yellowing 
of the oil itself. And it is the pigments which require the 
largest proportion of oil for grinding which exhibit in a 
marked degree the phenomena in question. 

A second action between a pigment and the oil with 
which it has been ground is the peculiar gelatinous or 
* livery ' condition quickly assumed by some oil-paints. 



64 OIL IN PAINTS 

This change is particularly noticeable with the cochineal 
and madder lakes. I have succeeded in obviating it, by 
carefully drying the pigments at a temperature just under 
ioo° C, before grinding them with oil, and by substitu- 
ting for raw linseed oil a mixture of the ' manganese oil,' 
described in the present chapter, with some poppy oil. 
Those pigments which dry easily should be ground with 
more of the latter oil, those which dry with difficulty with 
more of the former. Sometimes pigments harden quickly 
in the tube itself ; this change is due either to the siccative 
character of the pigments, or to the introduction of an 
actual * dryer,' or to the too copious use of a strongly sic- 
cative oil with those pigments which are naturally slow 
in drying. 

The third action between a pigment and the oil with 
which it has been ground appears to be of a distinctively 
chemical nature. The most striking example of it known 
occurs with flake-white. When normal flake-white, that 
is hydrato-carbonate of lead, is ground in oil and after- 
wards exposed to the air, it gradually becomes very 
hard — much harder than the great majority of other oil- 
paints under the same conditions, zinc-white for example. 
It is not the hardness of the lead-compound plus the 
hardness of the oxidized oil, but a hardness combined 
with toughness of a higher order. As those varieties of 
white-lead which consist wholly of the carbonate do not 
possess this quality in anything like the same degree, so 
it must depend upon the lead hydrate which is intimately 
associated with the carbonate in typical white-lead. It 
has been usual to conclude that the phenomenon is due 
to the formation of a lead soap, a linoleate of lead, by the 
interaction of the free acids in the oil with some of the 
lead hydrate. This view is supported by some, yet hardly 



ACTION OF PIGMENTS ON OILS 65 

decisive, experimental evidence. Thus the longer the oil 
and the lead-white remain in contact the more marked is 
the change, especially if the temperature be raised some- 
what above the normal. If a collapsible tube, filled with 
ordinary flake-white ground in oil, be tightly closed so as 
to exclude the air and then be submersed, in water kept 
hot, for a few days, the change in question is hastened. 
Consequently it becomes impossible to extract from the 
paint so treated, by means of ether or other suitable 
solvent, quite the amount of oil originally present. One 
could understand this result had the paint been allowed 
to absorb oxygen from the air, when some linoxine, in- 
soluble in most solvents of oil, would have been pro- 
duced. Whatever the action may be, and whatever the 
true explanation, the phenomenon is beyond question 
Further reference to this subject will be found in Chapters 
XIII. and XXIII. 

A fourth action between a pigment and the oil with 
which it has been ground is occasionally observed with 
certain colours of organic origin, which actually dissolve 
in and stain the oil. Bitumen, gamboge, and several 
alizarin preparations exhibit this phenomenon. 

2. The different amounts of oil required by different pig- 
ments may now be considered. As a rule, the densest or 
heaviest pigments require the least oil. A few pigments 
require an excess of oil in order to protect them from 
moisture or other injurious agents. Different authorities 
do not agree at all closely as to the amount of oil needed 
to make a workable oil-paint from the same pigment. 
The following list gives the weight required by 100 parts 
in weight of 22 pigments : 



66 



OIL IN PAINTS 







According to 


According to 


Name of Pigment 


C. 


Roberson and Co. 


Winsor and 






(1901) 


Newton (1901) 


White Lead - 




- 16 - 


- 15 


Zinc White - 




- 19 - 


- 23 


Aureolin - 




- 71 - 


- 49 


Chrome Yellow 




- 35 - 


- - 56 


Cadmium Yellow 




- 37 - 


- - 67 


Yellow Ochre - 




- 59 - 


- - 63 


Raw Sienna - 




- 147 - 


- 240 


Vermilion 




. _ - 


- 23 


Light Red 




. 69 - - 


- 70 


Madder Lake - 




- 103* - - 


- 55 


Terre Verte - 




- 49 - 


- - 87 


Viridian - 




- 56 - - 


- 52 


Prussian Blue 




- 72 - 


- - 78 


Cobalt Blue - 




- 50 - 


- 90 


Ultramarine (artificial) - 34 - 


- 43 


Raw Umber - 




- 97 - 


- 95 


Burnt Umber 




- 97 - 


- - 87 


Bitumen - 




. _ . 


- 127 


Brown Madder 




- 81 - 


- 93 


Vandyke Brown 




- 72 - 


- 94 


Burnt Sienna 




- 138 - - 


- 150 


Ivory Black - 




- 88 - 


- 112 



The discrepancies between the corresponding figures in 
the vertical columns are due, amongst other causes, to 
differences in the modes of preparation of the dry pig- 
ments ; to natural variations in the native earths em- 
ployed ; to the dissimilar standards of solidity or fluidity 
aimed at in the finished paint ; and to several other causes 
which it is needless to particularize, but amongst which 
may be named different modes of grinding and the em- 
ployment of different kinds of oil. 

The great differences in the above amounts of oil do not 
cause such serious results in the conduct of the process of 



Figure for rose madder. 



OIL IN PAINTS 67 

oil-painting as might have been expected at first, for they 
correspond in a measure to the relative bulks of the 
several pigments. We can use more copal or amber 
varnish to balance the excess of oil in some pigments, and 
so secure a uniformity of structure, texture, and rate of 
drying in the different parts of the work. It is, however, 
often convenient to remove some of the excess of oil from 
a pigment before using it, especially with the colours pre- 
pared by some makers.* This can be done by leaving 
the oil-paint on a pad of blotting-paper; but 3-inch cubes 
of plaster-of-Paris afford a far cleaner and surer method 
for the absorption of oil. It may be further remarked that 
the quantities of oil required by some of the pigments in 
the above table may be reduced by grinding them under 
greater pressure. Raw sienna, burnt sienna, and ivory 
black should be dried at 100° C. just before grinding, and 
then yield workable paints with less oil. The subsidence 
of vermilion from the oil in which it has been ground 
may in some measure be prevented by using ' manganese 
oil ' instead of raw linseed oil, and adding to it a small 
quantity of linoleate or oleate of alumina, or of beeswax, 
or of hard paraffin wax or ceresin, having a melting point 
not under 65° C. Some artists find it a good plan to keep 
their tubes of vermilion and of other heavy pigments in 
an inverted position — that is, with the cap downwards. 

* Dr. H. Stockmeier, of Niirnberg, found the following per- 
centages of oil in certain oil-paints from different sources which he 
analysed : 

Flake- White (Robersonand 
Co.) ... - i6-2 



Light Red (Winsor and 
Newton) - - - 41 '9 



Burnt Sienna (Dr. Schoen- 
feld) - - - - 59 '2 

Chinese Ochre (G. B. 
Moeves) - - - 45 



CHAPTER VI 

RESINS, WAXES, AND SOLID PARAFFINS 

In commercial parlance resins are incorrectly termed gums. 
The true gums (Chapter VIII.) are either soluble in water 
or swell up in that liquid, but resins are not acted on by 
water. The term resin is used throughout the present 
volume in its proper sense, so that ' copal resin,' * mastic 
resin ' are spoken of, not ' gum copal,' ' gum mastic' All 
the resins used for making vehicles and varnishes are of 
vegetable origin; they contain besides carbon and hydro- 
gen a not inconsiderable proportion of oxygen. They are 
related to the hydrocarbons known as terpenes, present in 
many essential oils, but are of more complex constitution. 
Some resins, such as gamboge, contain gum and are called 
gum-resins ; others contain a hydrocarbon (or terpene, see 
Chapter XI.) or an aromatic acid, and are called balsams ; 
others are true resins, but even these rarely, if ever, con- 
sist of a single definite compound, but are mixtures of at 
least two, often of three, four, or five different bodies. 
Generally these constituents of true resins differ as to their 
degree of solubility in various liquids, such as alcohol, 
ether, spirit of turpentine, benzene, petroleum spirit, and 
heated fixed oils. They contain carbon, hydrogen, and 
oxygen, with occasionally a little sulphur, and are usually 
of an acid character, and are capable of forming soaps, 

68 



AMBER 69 

called resinates, with the alkalies. Resins differ much 
from one another, not only in solubility but also in hard- 
ness and in the temperature at which they melt. Those 
which are least soluble are generally those which are 
hardest, and which require the highest degree of heat to 
bring them into fusion. Most true resins contain, besides 
their proper resinous constituents, small quantities of 
colouring-matter, of water, of crystalline aromatic acids, 
and of a volatile hydrocarbon or terpene. All these im- 
purities, save the first, may be removed, generally with 
advantage, by the following treatment. The powdered 
resin is thoroughly mixed with a little water and placed 
in a large glass retort. A current of steam is then passed 
into the mixture until the terpene and volatile acids 
present have distilled over. To the contents of the retort 
carbonate of soda is added (i part for each 100 of resin). 
The mixture after agitation is allowed to cool and then 
filtered through a fine cotton cloth. The purified resin is 
then washed on the filter with distilled water, then dried 
in the air and finally in the water-oven : the air-bath and 
a temperature of 110° to 120° C. may be used for the 
desiccation of the harder resins. 

It might be thought that the subject of resins would be 
sufficiently discussed from the painter's standpoint by a 
description of three kinds — amber, copal, mastic. But it 
will be shown presently that copal and mastic are names 
given to several distinct substances, and that there are some 
other resins which cannot be excluded from our view. 

Amber is the most familiarly known of all the resins on 
account of its long use in its natural state for ornamental 
purposes. Amber beads have not infrequently been found 
in early British graves ; on the Continent these and other 
ornaments of amber have often been obtained from ancient 



70 AMBER 

interments. At Naples I was shown some years ago a very 
large number of antique fibulae carved out of this sub- 
stance : they had just been disinterred from Etruscan 
tombs. Such amber has often become brittle and far more 
soluble in the usual solvents, especially so far as regards 
the surface layers ; but in other instances the preservation 
of the properties of this resin has been complete. The 
chief localities where amber is found are the Prussian 
shores of the Baltic Sea (particularly between Konigsberg 
and Memel) and the neighbouring plains; it has been 
found in veins, and is regularly quarried. Some amber, 
much of it having a dark colour, is found near Catania, 
Sicily. Near Lemberg (Galicia in Austria) nodules of 
amber occur in rock. It occurs in several places in Den- 
mark, Sweden, Norway, and France. In the British 
Museum collection of minerals there is a fine mass from 
Cambridge. Excellent specimens occur in comparative 
abundance on the seashore at Southwold in Suffolk, and 
at several other places on the Suffolk, Norfolk, and Essex 
coasts. The dark fossil resin found in Birma, often in 
large masses, is not identical with Baltic and English 
amber. The same observation may be made with respect 
to the so-called ambers of Travancore in the East Indies, 
and of the Isle of St. Louis, Senegambia, Africa. In 
fact, amber, instead of being, as commonly stated, the 
fossil resin of a single species of tree of Tertiary age, has 
obviously been derived from no inconsiderable number of 
different plants. Goppert, so long ago as 1853, satisfied 
himself that at least eight species of plants besides Pinites 
siiccinifev have afforded this fossilized resin : he also 
enumerated 163 species of plants as represented by remains 
in amber ; many others have been since recognised. 
Amber has a specific gravity of about 1*07 ; its hard- 



AMBER 71 

ness is 2J on the ordinary mineralogical scale. In most 
of the usual solvents of resins it is either insoluble or but 
partially soluble. When heated quickly on a spatula it 
splits up and then fuses into a viscous liquid, the drops 
which are formed rebounding as they fall upon a cold sur- 
face : this behaviour serves as a distinguishing test be- 
tween amber and copal. When crushed amber is heated 
in a retort it fuses at about 280° C. (536° F.), gives off 
water, succinic acid, marsh gas, a mixture of liquid hydro- 
carbons (known as oil of amber), and, finally, at a very 
high temperature, a yellow substance having a 'wax-like 
consistence. Sulphuretted hydrogen and other sulphur 
compounds are also evolved in small quantity, for amber, 
like several other fossil resins, contains a little sulphur 
(sometimes J a part in 100) in organic combination. 
Amber breaks with a conchoidal fracture. When frag- 
ments of amber are being ground or powdered they emit 
an aromatic odour. On being rubbed amber becomes 
negatively electric in a high degree. 

It is probable that true amber consists mainly of a 
single resin (85 to 90 per cent, of the whole) represented 
by the empirical formula wC^QH^gO. Small quantities of 
two other resins which are soluble in alcohol and ether, 
of a liquid hydrocarbon, and of succinic acid, are associ- 
ated with the main constituent, which has received the 
mineralogical name 'succinite.' 

The classical names for amber were yjXeKTpov, lyncu- 
rium, electnim, and sticcinimi. In early mediaeval times 
amber was called vernix, a term which at first was applied 
also to sandarac, and later in the fifteenth century to san- 
darac only, when amber was designated as glas, or glassa. 
In modern French amber is distinguished from ambre gvis 
as amhre jaune, although it is also known as karabe and 



72 COPAL 

succin. It is the Bernstein of the Germans. The word 
* amber ' is probably derived, through the Spanish, from 
the Arabic anbar, a term applied to ambergris. 

Copal is a name given to a number of hard resins which 
vary not only in their degree of hardness, but also in their 
degree of solubility : they are the produce of many dif- 
ferent species, and even genera of trees, while the origin 
of several of the kinds still remains unknown. One of the 
hardest, palest, and best of all is known as Sierra Leone 
copal, from the port of collection and shipment. It has 
been identified as the resin produced by a tree, Copaifera 
Gtiibouriiana, which belongs to the sub-order Caesalpineae 
of the order Leguminosae. It is probable that the hard 
West African pebble copal is the resin of the same tree, 
but it occurs in rolled pebbles with an abraded surface, 
and is at least semi-fossil : it is collected from the beds 
of streams. Pebble copal has more colour than Sierra 
Leone copal, but yields as strong a varnish. The latter 
resin occurs in irregular rounded lumps or masses, gener- 
ally varying in size from that of a hazel-nut to that of a 
walnut. It is hard and elastic. It consists of at least 
two resins, one of which, present to the extent of 33 per 
cent., is soluble in absolute alcohol and in spirits of tur- 
pentine. The other resin constitutes nearly the whole of 
the remaining part of the copal, and becomes soluble in 
most of the usual solvents, as well as in hot linseed oil, 
when it has been previously heated to its melting-point 
or to a temperature of 180° to 221° C. (360° to 430° F.). 
Another process for rendering this and other kinds of 
copal soluble is reduction to a fine powder in the presence 
of water and the subsequent exposure of this powder to 
the air for several months, or even a whole year. The 
time requisite for this change may be shortened by keep- 



COPAL 73 

ing the powdered copal at a temperature higher than that 
of the ordinary atmosphere. More will be said as to this 
and other methods of increasing the solubility of copal in 
the chapter on Varnishes. 

Other species of the genus Copaifera yield similar but 
inferior resins to that produced by C. Guibourtiana, but 
C. Gorskiana is the source of Inhambane (near Mozam- 
bique) copal ; Benguela copal, Angola copal, and Gaboon 
copal are other sorts, varying in hue from straw-colour to 
a dull reddish-orange, produced in all probabiHty by 
different species of Copaifera. Much of the so-called 
Manilla copal is the produce of Agathis loranthi folia. 

Zanzibar copal is another hard and valuable resin of 
African origin : it is often called anime. It is produced 
by another leguminous tree, Trachylobium Hornemannia' 
num, which belongs to the same sub-order, Caesalpineas, as 
Copaifera. Most of this Zanzibar copal occurs in a fossil 
or semi-fossil state in the earth near the roots of the trees, 
or in places where the trees have formerly stood. This 
fossilized resin is covered when dug up with a semi- 
opaque, rough, and dull-brown crust ; when this powdery 
coat is removed the remainder of the mass appears of a 
transparent yellow colour, with a surface covered with 
small rounded elevations like those on the rind of an 
orange : this is spoken of as ' goose-skin.' Many of the 
pieces are flat and tabular, with a thickness of a quarter 
of an inch or more. The same resin, when occurring on 
the bark of the living trees of the same species of Trachy- 
lobimn, presents a smooth and glossy surface ; it is not so 
hard as the fossil variety. Zanzibar copal melts at a 
higher temperature than Sierra Leone copal, and is very 
hard. In order to render it soluble it may be treated in 
the same manner as the Sierra Leone copal. Its chemical 



74 COPAL 

nature requires further study. The varnish made with 
Zanzibar copal, though darker in colour, must be re- 
garded as at least equal in strength and durability to that 
prepared with Sierra Leone copal. 

A third resin, sometimes designated as copal, some- 
times as anime, is produced by another leguminous tree, 
Hymencsa cotirbaril, a native of Brazil and other countries 
of South America. It is rather softer and more soluble 
than Zanzibar copal. The copal of Madagascar comes 
from another species of the same genus, H. verrucosa. A 
Mexican copal is probably the resin of an allied species. 
The resin from H. courharil is generally known as West 
Indian copal ; fine specimens have been received from 
Demerara. 

The Bungo tree of Sierra Leone, Daniellia thurifera, 
affords a resin of inferior quality. It is probable that the 
same leguminous tree is the source of some of the Niger 
and Sudan copals. 

A rather hard resin of comparatively recent introduction 
is Kauri or Cowdi copal, produced by the Cowdi pine of 
New Zealand, Dammara australis. This is a coniferous 
tree belonging to the tribe Araucariae. The largest masses, 
some of them occasionally over lOo pounds in weight, are 
found in the earth in many places far from those in which 
the trees now grow. Kauri resin usually becomes more 
transparent and yellower by keeping. It is generally 
somewhat whitish, or streaked with opaque bands, when 
first found. It is cleaned and scraped and then sorted 
into several qualities. Great quantities were imported 
into England for some years, and for a time it was largely 
employed as the basis of most of the so-called copal 
varnishes, on account of its abundance, its low price, and 
its easy manipulation. But the varnish which it yields, 



DAMMAR 75 

or of which it constitutes the chief resinous component, 
is inferior in hardness, toughness, and durabihty to that 
made from Sierra Leone copal or Zanzibar copal. 

Kauri resin is sometimes spoken of as dammar, but this 
name properly belongs to the resins produced by other 
trees, not by Damniava austvalis. White or Singapore 
dammar is the resin of Damniava ovientalis. It is soft, and 
may be scratched even by mica. ' Sal dammar ' is produced 
by Shorea robustay the sal tree, widely distributed in India. 
This resin, though soft, yields a good flexible paper 
varnish. The tree belongs to the Dipterocarpeae. Vateria 
indicay another Dipterocarp, yields piney resin or white 
dammar : a similar resin is produced by another species, 
V. acuminata^ a Ceylon tree. Several kinds of Hopea {H. 
micrantha, H. odorata, etc.), which belong to the same 
natural order, yield pale, transparent resins which are a 
trifle harder than that of the sal tree. Black dammar or 
Tinnevelly resin is produced by Canariiim stricUim ; it is of 
very inferior quality. This tree belongs to the Burseraceae : 
several kinds of elemi resin are also furnished by plants 
belonging to the same natural order. These elemis are 
soft, sticky resins, occasionally employed in varnishes to 
prevent them from becoming brittle and cracking. They 
contain essential oils and other aromatic bodies, and vary 
very much in composition and properties, although they re- 
semble one another in their solubility in boiling alcohol and 
in their easy alterability. They are unsatisfactory resins. 

The resin first known as sandarac was probably juniper 
resin, although the name was also applied to amber. It is 
spoken of by the older authorities on painting as having 
a red colour. Its hue is a dull reddish orange, and it yields 
a dark-brown varnish when dissolved by the aid of heat in 
a drying oil. The effect of this varnish in imparting an 



76 MASTIC 

agreeable warm tone to pictures painted in tempera is very 
evident, when the cold aspect of an old Italian unvarnished 
tempera picture is compared with the glowing colour of a 
painting which still retains its original sandarac varnish. 
The resin now called sandarac is produced by another 
coniferous plant [Callitris quadrivalvis), a native of Algiers. 
It is a pale yellow resin, when fresh resembling mastic in 
colour, but becoming yellower with age. It is brittle and 
melts easily. When finely powdered and sifted it forms 
one of the kinds of pounce used in preparing the surface 
of parchment and vellum for writing and illuminating. 
It dissolves in alcohol and in acetone, incompletely in 
petroleum spirit and benzol. 

There is one more resin which requires mention. This 
is mastic. The best and most important sort of mastic is 
produced by a small tree {Pistacia Lentiscus), belonging to 
the cashew-nut order or Anacardiacese. This tree occurs 
in Scio and other islands of the Greek Archipelago. Mastic 
exudes in the form of tears from incisions made in the 
bark. It occurs in small pea-like masses, and presents 
when fresh a very pale straw-colour. It is so fragile that 
it may be crushed to powder between the fingers. It has 
an aromatic odour, and dissolves completely in boiling 
alcohol and in spirits of turpentine. Its melting-point is 
low, on an average about iio° C. It contains, besides its 
resinous constituents, a small quantity of a volatile essen- 
tial oil (a terpene) and of moisture. It yields a tender 
but glossy varnish, largely employed for the final protec- 
tion of pictures in oil. This varnish yellows with age, 
and becomes fragile and fissured. 

Resins, sometimes called mastics, are produced by other 
trees of the same genus. These resins, which are of no 
value for artistic purposes, are : 



COPALS 77 

Indian mastic from Pistacia cahdica. 
Bombay mastic from P. Khinjak. 
Pistachio mastic from P. Terebinthus. 

In the following table, compiled from the results of 
Bottler, are comprised some particulars concerning twelve 
of the resins commonly called ' copals.' In the first 
column the names are given, in the second the melting- 
points, in the third the relative hardness (12 being the 
hardest), and in the fourth and last column the degree of 
solubility (xii being the least soluble). The specific 
gravity of these copals depends so much upon the relative 
freedom of the several kinds from cavities and bubbles 
that the figures for this character are not included in the 
table. It may, however, be mentioned that all these 
resins are rather heavier than water, their specific gravi- 
ties ranging from i '035 to i -07. 



Name of Copal 


Melting-point 


Hardness 


Solubility 


Zanzibar - 


- 275° C. 


12 


xii 


Red Angola 


- 315 - 


II 


ix 


Pebble Copal - 


- 230 - 


10 


xi 


Sierra Leone - 


- 195 ■ 


9 - 


V 


Yellow Benguela 


- 180 - 


8 - 


vii 


White Benguela 


- 185 - 


7 - 


X 


Congo 


- 190 - 


6 - 


iv 


Manila 


- 145 - 


- 5 - 


ii 


White Angola - 


- 245 - 


4 - 


i 


Kauri 


- 150 - 


3 - 


iii 


Demerara 


- 90 - 


2 - 


viii 


Brazilian - 


- 95 - 


I 


vi 



All these numbers are approximative only ; and the 
valuation of these resins for varnish-making ought to 
take into account other properties not here recognised, 
such as toughness after as well as before heating and 
solution, liability to darkening in colour by lapse of time, 
and durability. 



78 VENICE AND STRASBURG TURPENTINE 

Turpentines, Oleo-Resins, and Balsams. — There is a group 
of substances, many of them derived from coniferous 
plants, which are, or have been, included under the term 
balsam. Strictly speaking, this designation should be 
limited to those resinoid exudates which contain benzoic 
or cinnamic acid, while the term oleo-resin, or, better still, 
the term turpentine, should be given to those soft and semi- 
liquid natural exudates which consist of terpenes asso- 
ciated with bodies of resinous character. The word 
turpentine is, however, so generally connected with the 
volatile hydrocarbons (terpenes) distilled from these 
exudates, that it should be clearly understood that the 
three vegetable products hereunder described are of 
natural, not artificial, origin. It is in consequence 
of the preservative influence upon certain pigments 
which has been assigned, not without experimental 
confirmation, to these bodies that they are noticed 
here. 

Venice Turpentine. — Under this name the resin of the 
common larch is now known. It comes chiefly from Tirol. 
Recent examination has shown it to consist mainly of three 
groups of compounds, namely, about 63 per cent, of 
resinous acids, 20 per cent, of terpenes, and 14 per cent, 
of resins. The best specimens are never quite so clear 
and free from colour as those of the next product to be 
described. 

Strasburg Turpentine is derived from Abies pectinata, the 
silver-fir, the best quality coming from the Italian side 
of the Tirolese Alps. It contains about 57 per cent, of 
resinous acids (not identical with those in larch-turpentine), 
28 per cent, of terpenes, and 13 per cent, of resins. This 
turpentine is the true Olio d'Abezzo of Italian writers, and 
when dissolved in a terpene was used as a varnish for 



WAX 79 

pictures in tempera and oil, and for the special protection 
of verdigris and of some other dangerous pigments. Some 
specimens of this turpentine are beautifully clear and 
colourless. It is decidedly superior to larch turpentine, 
with which it has no doubt been often confused, and to 
Bordeaux turpentine, obtained from Pinus Pinaster. The 
chemical study of the olio d'abezzo has at present thrown 
no light upon the specially protective or locking-up 
qualities which are claimed for this turpentine. 

Canada Balsam^ from Ahies halsamea, much resembles 
Strasburg turpentine. The resinous acids which consti- 
tute three-fifths of its weight are said to be different from 
those already mentioned as existing in the turpentines 
from the larch and silver-fir. 

Wax. — The true waxes, unlike the oils described in 
Chapter V., are not glycerides, and do not therefore yield 
glycerin when they are saponified — that is, turned into 
soaps by the action of alkalies. Ordinary beeswax is the 
best known, and probably the most important of all the 
different kinds ; but very few experiments have been made 
as to the utiHzation of exotic and vegetable waxes in the 
processes of painting. Crude beeswax requires purifica- 
tion and bleaching in order to fit it for artistic use. The 
first operation consists in melting the wax at nearly the 
lowest temperature possible, and then pouring it in a 
slender stream into a cold saturated solution of alum, 
agitating the latter all the time. The granulated wax thus 
prepared may be bleached by exposure for several days on 
linen cloths to the action of the sunlight and dew; or it may 
be treated with dilute chromic acid solution, or with hydro- 
gen peroxide. All these processes succeed better when 
the wax is in the form of thin sheets or ribbons. The 
bleached wax, after thorough washing and drying, is to 



8o WAX 

be re-melted. Its hardness is increased and its melting- 
point raised by the above treatment. 

Bleached beeswax melts at 62° or 64° C. (144° or 
147° F.). It consists of four distinct substances, not 
present in all samples in the same proportions. By boiling 
wax with strong alcohol a substance called myricin 
(myricyl palmitate) is left undissolved. The dissolved 
portion is the larger ; the bulk of it, which crystallizes 
out as the alcohol cools, was formerly called cerin. It is 
a mixture of two fatty acids. The cold alcohol still 
retains a small quantity of a fourth substance. 

Beeswax, by long-continued exposure to atmospheric 
influences, disintegrates and partially perishes by oxida- 
tion. It is a constituent of Gambier-Parry's spirit-fresco 
medium, into which it is introduced in order to impart a 
matt appearance to the painting. Excellent examples of 
the use of melted wax as a binding material for pigments 
may be seen in the National Gallery and the Victoria 
and Albert Museum. They are encaustic portraits, exe- 
cuted probably in the second and third centuries of our 
era, and were discovered by Professor W. M. Flinders 
Petrie, in the Hawara Cemetery, Fayum, Egypt. The 
pigments were mixed with wax and laid on in the melted 
state. The wax having become disintegrated in the 
course of centuries has been re-melted, some fresh wax 
having been added in several instances. 

Wax is abundantly distributed in the vegetable world ; 
its production is, in many cases, stimulated by the 
attacks of insects. Thus, Chinese wax is produced by 
the puncture of Coccus Pela, living on Ligustrum lucidum 
and Fraximis chinensis. Chinese wax, which melts at 
82° C. (180^ F.), consists almost entirely of cerotyl 
cerotate. Brazilian or Carnaiiba wax occurs naturally 



PARAFFIN WAX 8i 

in thin films on the leaves of a palm {Copernicia cerifeva) ; 
it melts at 84° C. (183° F.). Japanese or Ibota wax is 
probably produced by the attacks of a coccus on Ligustvum 
Ibota; it melts at 42° C. (108° F.). 

Paraffin wax, hard paraffin, solid paraffin, and ceresin, 
are names given to certain mixtures of hydrocarbons 
occurring in native petroleum and in the * mineral wax ' 
called ozokerite, and also in the tars produced by the 
destructive distillation of wood, peat, lignite, bituminous 
shales, and coals. The liquid hydrocarbons which 
accompany the paraffin wax are described so far as 
necessary in Chapter XI. under the head of Solvents. 

Paraffin wax, so far as its main or fundamental con- 
stituents are concerned, contains no oxygen, and is a 
mixture of several of the least alterable of all organic 
compounds ; very few chemical reagents have any action 
at all upon it. On this account it presents for artistic 
purposes a marked superiority over beeswax or any 
vegetable wax. Of the hydrocarbons occurring in large 
quantity in paraffin wax the best known are those to 
which the chemical formulae CggH^g, C24H50, CggHgg, 
C27H56, CggHgg, and C^qHqq belong. The melting-point 
of paraffin wax oscillates within wide limits, say, from 
30° to 80° C. The higher the melting-point the harder, 
the heavier, and the less crystalline is the material. For 
artistic purposes, hardness and the absence of a tendency 
to separate from solution in the form of large crystals 
are desirable properties. Unfortunately the hardest 
paraffin waxes of high melting-point are much less 
soluble in oils, terpenes, and varnishes than the softer 
varieties, and thus their usefulness is limited ; they are 
also somewhat yellowish in hue. I have, however, 
found that a pure paraffin wax from the Bathgate shale, 

6 



82 PARAFFIN WAX 

having the melting-point of 65-5° C. (150° F.), answers 
every purpose. It is sufficiently hard and but indistinctly 
crystalline, and yet may be dissolved in fair abundance 
by the usual solvents. It is convenient to preserve it 
for use in the form of small flattened globules, which 
are easily prepared by melting the substance and pouring 
it drop by drop on to the surface of a large sheet of glass 
previously moistened by breathing upon it. When these 
drops are shaken in a bottle they rattle like small pebbles, 
and do not mark the glass ; when the softer soHd paraffins 
are thus treated, they fall with a thud, and leave streaks 
and spots upon the interior surface of the vessel. This 
difference of deportment affords a ready means of dis- 
tinguishing between a paraffin wax suitable for artistic 
uses and one which had better be rejected. 

The manufacture or isolation of hard paraffin and its 
purification are not described here. The processes em- 
ployed — distillation, treatment with oil of vitriol, frac- 
tional crystallization from solvents, etc. — involve the use 
of complex apparatus. It may, however, be here stated 
that commercial hard paraffins vary somewhat in purity. 
Those obtained from mineral wax or ozokerite are nearly 
free from oxygen compounds ; while those derived from 
the products of the destructive distillation of shales, coal, 
etc., sometimes contain as much as 3 per cent, of oxygen, 
indicating the presence of other bodies besides hydrocar- 
bons. Some of these bodies are of an acid nature ; these 
may be separated by repeatedly boiling the commercial 
paraffins in question with a 5 per cent, solution of caustic 
potash. The following table shows the relations subsist- 
ing between the melting-point and the specific gravity 
(at 20° C.) of six different samples of hard paraffin, 
generally known as ceresin, from ozokerite : 







PARAFFIN WAX 




83 


No. oj 


Melting- 


Specific 


No. of 


Melting- 


Specific 


Sample 


point 


Gravity 


Sample 


point 


Gravity 


I - 


- 56° c. - 


- 0-912 


4 - • 


72° C. - 


- 0-935 


2 - 


- 61° - - 


- 0-922 


5 - 


76° - - 


- 0-939 


3 - 


- 67° - - 


- 0-927 


6 - - 


82° - 


- 0-943 



A sample of ceresin made from ozokerite was furnished 
to meat my request by the late J. Calderwood, of Price's 
Patent Candle Company. It has a setting-point of about 
156° F. (69° C), and is almost non-crystalline in appear- 
ance. It possesses, however, a somewhat greasy feel and 
a slight yellowish hue. I find by experiment that this 
ceresin, with a small admixture of a refined paraffin 
(from the same manufacturers) having a melting-point 
of 147° F., forms an excellent substitute for the hard 
paraffin wax (melting-point 150° F.), from Bathgate shale, 
described on a preceding page, and unfortunately no 
longer to be met with in commerce. 

Hard paraffin wax may be used in the preparation of 
painting mediums as a substitute for beeswax ; for pre- 
venting the separation of heavy pigments, such as ver- 
miUon, from the oil in which they are ground ; and for 
the preparation of certain painting-grounds. 

U In practice it has been found that far smaller quan- 
tities of beeswax than of paraffin wax are required to 
prevent the subsidence of heavy pigments from the oil 
in which they have been ground. Moreover, the working 
of paints containing a small quantity of beeswax is more 
agreeable than is the case with those into which paraffin 
wax has been introduced. 



CHAPTER VII 

YOLK AND WHITE OF EGG ; SIZE ; GLUE 

The materials described in the present chapter owe their 
peculiar properties — at least, in great measure — to the 
presence of chemical compounds which contain the ele- 
ment nitrogen. Now, this element is not a constituent of 
any of the artists' materials already described, nor, indeed, 
of any others, except a few pigments, such as aureolin, 
Prussian blue, and indigo. The presence of nitrogen in an 
organic compound is very often accompanied by a measure 
of instability, or proneness to change; the nitrogenous con- 
stituents of eggs, and of size, afford illustrative examples. 
Another source of weakness in the composition of the 
nitrogenous constituents, both of the white and of the yolk 
of eggs, lies in the presence of another element — namely, 
sulphur. Part of this sulphur readily leaves the original 
substance, yielding simpler compounds, such as sulphur- 
etted hydrogen, and ammonium sulphide, which possess 
the objectionable property of discolouring many of the 
metallic pigments used by artists. On the other hand, all 
these nitrogenous bodies are susceptible of coagulation, 
whereby they become insoluble, and very much less prone 
to change. Indeed, the majority of them may be turned 
into a substance which is virtually leather, a material 
which resists decay in the most marked manner. This 

84 



WHITE OF EGG 8$ 

tanning operation may be readily effected by treating the 
substances in question with a solution containing tannin, 
the active ingredient of oak-bark, sumach, nut-galls, etc. 
We will first consider the composition of the yolk and 
white of ordinary hen's eggs. The percentage proportions 
are, on the average 



v-> 




Yolk 




White 


Water - 


- 


- 51-5 - 


- 


- 84-8 


Albumen, Vitellin, 


etc. 


- 15-0 - 


- 


- I2'0 


Fat or Oil - 


- 


- 22 -o - 


- 


0-2 


Lecithin, etc. 


- 


- 90 - 


- 


- trace 


Mineral Matter - 


- 


i-o - 


- 


- 07 


Other Substances 


- 


- 1-5 - 


- 


- 2-3 



The white, it will be seen, is characterized by the 
presence of 12 parts per hundred of albumen, which is in 
solution in the ropy Hquid. When this solution is heated 
to a temperature considerably below that of boiling water, 
the albumen becomes insoluble, and is said to be coagu- 
lated ; it is not capable of being again dissolved in its 
original menstruum. Solutions of tannin, corrosive subli- 
mate, and many other compounds, inorganic and organic, 
produce a similar effect. But egg-white is not a pure 
solution of albumen. For all practical purposes in the 
arts, it may be sufficiently freed from extraneous matters 
in the following manner : The necessary number of 
* whites ' are mixed in a wide-mouth stoppered bottle, with 
twice their bulk of water, and shaken up thoroughly ; 
then a slip of yellow turmeric-paper is dropped into the 
mixture. Drop by drop weak acetic acid is poured in, 
until the reddened turmeric-paper ha.sj7Lst, or nearly, re- 
gained its original yellow hue. In this way the alkaline 
reaction of the liquid is almost neutralized, and it becomes 
thinner. After further agitation, the mixture is poured 
upon a piece of well- washed muslin in a funnel. The 



86 COAGULATION OF ALBUMEN 

clear liquid which drops through has been freed from 
membranes, etc., and contains nearly 4 per cent, of albu- 
men. It may be concentrated by cautious evaporation 
at a temperature not exceeding 50° C. The albumen 
which it contains is a very complex substance, containing, 
besides carbon, hydrogen, nitrogen, and oxygen, about 
1*6 per cent, of sulphur. A solution of albumen spread 
upon glass, and allowed to dry slowly at the ordinary 
temperature, leaves a residue of albumen in the form of a 
nearly-transparent film. This, when quite dry, is brittle, 
and easily cracks. If, before it be quite dry, it be heated 
to 70° or 75*^ C, it cannot be again dissolved by water, 
having been converted into the insoluble form. In this 
condition it is much less prone to change. It will now 
be seen how powdered pigments, if ground up with albu- 
men solution and then used in painting, may be made to 
cohere, and also to adhere to the painting-ground of cloth, 
paper, or plaster, on which they have been spread. And 
afterwards, by simply heating the work sufficiently, the 
whole coloured layer may be rendered insoluble and irre- 
movable by water. Advantage may also be taken of the 
action of tannin on albumen to secure the same result 
— the coagulation of the albumen. We may coat a piece 
of fine linen cloth with albumen-solution, and before it is 
quite dry we may paint upon it with pigments which have 
been previously ground up with a weak solution of tannin. 
If the work be carefully done, the colours will, when dry, 
be found to have been fixed by the reaction between the 
tannin and the albumen. If, however, the pigments be 
laid on somewhat quickly, it may be found necessary to 
give the whole surface a final coat of albumen-solution. 
We have dwelt at some length upon this employment of 
tannin, or of heat, to secure the coagulation of albumen, 



YOLK OF EGG 87 

because it serves to illustrate the way in which paintings, 
executed with egg-yolk, or size, as a medium, may be 
fixed. For, as we shall now proceed to show, egg-yolk 
and size possess many characters in common with 
albumen-solution. 

But the yolk of an egg contains other substances besides 
albumen. First of all, the albumen present is accompanied 
by another similar compound called vitellin, which re- 
sembles it in composition and properties, and which, for 
our present purpose, we need not further describe, except 
so far as to state that, unlike albumen, it is not soluble in 
water. Of albumen and vitellin, taken together, egg-yolk 
contains, as we have seen, not less than 14 or 15 per cent. 
But egg-yolk is something more than a solution of these 
two similar bodies. It is, in fact, an oily emulsion, in which 
innumerable minute globules of a thick, fatty oil are sus- 
pended in an albuminous solution. And, moreover, the 
amount of this oil is large ; there is about 22 per cent of 
it, and associated with this oil there is no less than 9 per 
cent, of a curious compound called lecithm, which has 
many of the physical properties of a fat. It seems to be 
a triglyceride, including two fatty-acid radicles and one 
phosphoric acid radicle. Associated with lecithin there is 
a nitrogenous basic compound. Although lecithin re- 
sembles oils and fats in its behaviour to most solvents, it 
yet differs from them in this one particular, that it is very 
hygroscopic and swells up in water, forming a kind of 
emulsion. Now, 9 parts of lecithin with 22 parts of oil 
make up nearly one-third of egg-yolk, or 31 parts of oily 
or fatty matter per 100, as against 15 parts of albuminoid 
matter, or vitellin and albumen taken together. Hence 
it happens that egg-yolk, the usual vehicle for pigments in 
the best kind of tempera-painting, must be regarded as 



88 SIZE AND GLUE 

essentially an oil-medium. As it dries, the oil hardens, 
and remains intimately commingled with the albuminous 
substances left behind on the evaporation of the water 
present. These albuminous substances coagulate and 
become insoluble in the lapse of time — a change greatly 
accelerated by the old practice of exposing the finished 
tempera picture to sunshine previous to varnishing it. 

Size and glue may be considered together. They consist 
of two distinct yet similar compounds, known respectively 
as gelatin and chondvin. These bodies consist of carbon, 
hydrogen, nitrogen, and oxygen ; and, when pure, they 
contain no sulphur. They are soluble in hot water, yet 
are coagulable by tannin and by some other compounds, 
organic and inorganic. Chondrin is thrown down from its 
solution by alum, and, indeed, by several compounds which 
do not precipitate gelatin. The latter body is obtained 
from skin, tendons, and bones. These organized structures 
contain a substance called ossein, or collagen, which, under 
the influence of boiling water, dissolves, becoming changed 
into gelatin. This conversion occurs more quickly when 
the process is performed under a pressure somewhat 
greater than that of the atmosphere, and, therefore, at a 
temperature rather higher than ioo° C. In this way the 
transformation of the organic tissue of ivory, bone, vellum, 
parchment, fish-bladder, etc., into gelatin may be readily 
effected. The purity of the product depends, in part, upon 
the care with which the raw materials have been selected 
and cleansed, in part upon the temperature and the dura- 
tion of the extraction. If the temperature be too high, or 
the boiling be much prolonged, the gelatin produced is 
transformed partially into a substance which does not 
gelatinize when its aqueous solution is cooled, Chondrin 
is obtained from cartilage, which consists mainly of carti- 



SIZE AND GLUE 89 

lagin, or chondrigen, by the same process which changes 
collagen into gelatin. A hot solution of chondrin gelatin- 
izes on cooling just like one of gelatin ; but it does not 
yield, with the same amount of substance, so firm a jelly. 
Size, glue, and commercial gelatin, consist of mixtures of 
gelatin, chondrin, and the non-gelatinizing substances 
produced by the long-boiling or the over-heating of their 
solutions. Isinglass, vellum, and ivory-dust yield a size 
which contains nothing but gelatin and a little mineral 
matter ; the darker and stickier kinds of glue contain 
many impurities, having been made from very varied 
materials, such as ox-hoofs, horseflesh, old leather, etc. ; 
they often contain sulphuric acid. 

In selecting a size for artistic use, the special purpose 
in view will indicate whether an insoluble (in cold water) 
and strongly-gelatinizing, or a partially soluble and very 
adhesive one should be selected. The former is less liable 
to crack when dry than the latter. The very fine gelatins 
used in photography will often be found suitable. A few 
experiments, with cold water and then with hot, will soon 
reveal the peculiarities of the samples submitted to ex- 
amination. As caustic lime, caustic soda, chloride of lime, 
sulphurous acid, and certain mineral acids, are frequently 
employed in the manufacture of size, glue, and gelatin, it 
is absolutely necessary to ascertain, before using these 
materials in any process of painting, their freedom from 
free acids, free alkalies, or bleaching agents. A hot-water 
solution of the material must not redden blue litmus-paper, 
nor bleach dahlia-paper, nor embrown tumeric-paper. 

Glue and size may sometimes be purified and improved 
by cutting up the solid or gelatinous mass into small 
pieces, soaking them in distilled water for a few hours, 
and then pouring off the liquid before dissolving them . 



90 PRESERVATION OF EGG-YOLK 

The temporary preservation from putrefaction of the 
solutions of the substances described in the present 
chapter, may be effected in several ways. A lump of 
camphor, or a few drops of eugenol (from oil of cloves), 
is generally sufficient. I have preserved the egg-yolk 
medium for tempera-work for many days in an agreeable 
condition for use by the following plan : A saturated 
solution of eugenol in 5 per cent, acetic acid is first made, 
then this is added, drop by drop, with constant agitation, 
to the required number of yolks in a wide-mouth bottle, 
the point at which to stop further addition being learnt by 
the change of colour of a slip of turmeric-paper. When 
this paper just regains its original yellow colour, which 
was turned brownish-red by the yolks, no more acetic 
acid is wanted. Any water needed for thinning the 
medium may now be added, together with a lump of 
camphor, which will remain floating on the surface. 



CHAPTER VIII 

GUM, STARCH, DEXTRIN, HONEY, AND GLYCERIN 

The term gum is properly applied to a number of non- 
crystalline, structureless substances, of vegetable origin. 
They consist essentially of so-called hydrates of carbon, 
and are either soluble in cold water, or swell up when left 
therein for some time. The only gum of any importance 
in painting is gum-arabic. This name is not, however, 
exclusively applied to one variety only ; it is given to the 
gums which exude from several species of Acacia. For 
instance, Acacia arabica furnishes the Morocco, Mogador, 
Brown Barbary, and East Indian gums of commerce. 
But it should be noted that, although A . arabica is a native 
of India, and is grown to some extent in many parts 
of that empire, the gum it yields is rarely, if ever, exported 
thence, the so-called East Indian gum-arabic being really 
taken from Red Sea ports to Bombay, and thence re- 
shipped to Europe. Acacia arabica, however, does not 
furnish a strong and durable gum, and it is from another 
species, A. Senegal, that we obtain the gum employed as a 
binding material for water-colours. This gum is known 
commercially as Kordofan, picked Turkey, white Sennaar? 
and Senegal gum. The tree which yields it is a native of 
Senegal and the Sudan ; it grows to a height of twenty 
feet. The supplies which come from Kordofan are of the 

91 



92 GUM SENEGAL 

finest quality, but all the grades of gum from A . Senegal 
are superior to the produce of A . arabica in their greater 
dryness, density, and adhesiveness, as well as in the 
smaller amount of mineral matter which they contain. It 
may be added in this place that, according to some authori- 
ties, a part of the gum Senegal of commerce is produced 
by other species of Acacia besides A. Senegal, such as 
A . Adansonii, A . albida, A. dealbata, A . nilotica, A. Vevek, etc., 
and even from species of Kaya, Spondias, and Stevcidia. 
Suakim gum, the produce oi Acacia stenocavpa and A. Seyal, 
varies greatly in quahty, but is largely imported into 
England, and much used, though not generally available 
for fine work. 

Gum consists mainly of arabin, a mixture of the salts 
of an acid called arable acid, and of the free acid itself. 
The salts are those of the three bases — potash, lime, and 
magnesia ; water is also present. It is probable that, in all 
varieties, even of the finest gum Senegal, other organic 
acids, besides arable acid, are present. An analysis of a 
fine specimen of picked ' Turkey gum ' gave 15 per cent, 
of water, and 2*8 per cent, of ash, leaving 82-2 per cent, 
for the arable and other allied acids and organic matters. 
The arable acid was formerly expressed by the formula 
^i2^22^iij ^^^ ^^^ experiments of O'Sullivan indicate a 
much more complex composition (CggH^^gOyJ. 

Gum from Acacia Senegal, the only sort which ought to 
be employed in painting, should be nearly free from colour, 
and should dissolve in cold water without leaving an appre- 
ciable residue. Its watery solution should be clear, and 
should give no colour with tincture of iodine, but an abun- 
dant precipitate with ammonium oxalate solution. If 
iodine produce a purplish colour, adulteration with dextrin 
is indicated ; the white precipitate thrown down by the 



GUM TRAGACANTH 93 

oxalate shows the presence of calcium, a constant con- 
stituent of the genuine gum. I have found that the 
samples of gum sold to me as gum Senegal were of a more 
pronounced yellowish colour than those bought as gum- 
arabic and best Turkey : the lumps varied more in size, 
often contained air-bubbles, and were less fissured. The 
adhesiveness and toughness of these samples, moreover, 
compared favourably with these properties as exhibited 
by the finest and whitest ' Turkey gum ' obtainable. 

For the preparation of water-colours, and for occasional 
use in the operations of painting, it is convenient to have 
at hand a standard solution of gum. This may be pre- 
pared by dissolving i ounce of the selected gum reduced 
to fine powder in 2 measured ounces of boiling distilled 
water. The powdered gum should be very slowly added, 
with constant stirring, to the boiling water. When the 
whole is dissolved, the liquid is allowed to stand for at 
least a day ; then it is decanted from any sediment that 
may have been deposited into a wide-mouth bottle with- 
out cork or stopper, but covered with a glass cap. It is 
well to allow a lump of camphor to float in it, or to add 
to it a couple of drops of eugenol, the active antiseptic 
constituent of oil of cloves : a still more effective pre- 
servative is /5-naphthol. 

Gum tragacanth is produced by certain leguminous 
shrubs belonging to the genus Astragalus. Amongst these 
may be named: A. giimmifer, A. eviostylm^ A. hvachy calyx, 
and A. adscendens. Its constituents include a small quan- 
tity of a gum soluble in cold water, a little starch and 
cellulose, and a large proportion of a mucilaginous body 
which swells up in cold water, but does not dissolve. 
The substance having these properties is a compound of 
carbon, hydrogen, and oxygen of very complex consti- 



94 



STARCH 



tution, which has been called hassorin. Gum tragacanth 
contains from 12 to 15 per cent, of water, and leaves 2 to 
3 per cent, of ash when burnt. A mucilaginous medium 
made with gum tragacanth may be used for painting on 
linen : it is not very easy to prepare so as to be of uniform 
consistency. A fairly good plan is to place the finely- 
powdered tragacanth in a bottle, and to add enough spirit 
of wine to moisten it : then add the required amount of 
water, and shake the mixture gently at intervals. Water 
containing no more than 3 or 4 per cent, of the gum con- 
stitutes a moderately thick mucilage. 

^ Tragacanth mucilage containing from |^ to 2 per cent. 
of this gum serves as a binding medium in the making of 
crayons for pastel work. 

Other gums are of small importance. They commonly 
contain much bassorin and but little arabin. The Aus- 
tralian wattle gums from several species of Acacia are 
perhaps thus constituted ; but if this be the case, the 
bassorin present in them seems to present some points of 
difference from the bassorin of tragacanth. Cape gum is 
produced by Acacia horvida : it is inferior to gum-arabic, 
as a substitute for which it is used in Cape Colony. 

Starch comes next in our list. This important food- 
substance occurs in commerce in a condition so nearly 
pure that there is no need to describe its character. For 
the limited uses to which it is put in artistic practice the 
uncoloured or white starch should be selected. The 
starch from rice, wheat, maize, or potatoes may be em- 
ployed indifferently. Arrowroot may also be used. The 
preparation of starch-paste does, however, require some 
care. The best plan is to thoroughly agitate 50 grams of 
the dry powdered starch with enough cold water to produce 
a liquid of creamy consistence, and then to pour this 



STARCH 95 

mixture slowly into a vessel in which about 300 cubic 
centimetres of distilled water is kept in steady ebullition. 
All but 2 per cent, of the starch will dissolve into a nearly 
transparent homogeneous paste : the quantity of starch 
must be reduced if a thin liquid be required. 

^ Although starch has not hitherto been much employed 
in painting, its merits are such as deserve a more extended 
use. As its constituent elements include neither nitrogen 
nor sulphur, it is, on the one hand, more stable and less 
liable to the attacks of micro-organisms than size, white 
of egg^ or casein ; while, on the other hand, its chemical 
inertness is such that there is no fear of its exercising 
any injurious effect on colouring matters. But ordinary 
starch paste, owing to its viscous character, is not very 
suitable as a binding material for pigments. However, 
by means of certain treatments, as with ozone, glycerin, 
or volatile acids, starch can be brought into a more soluble 
and Uquefiable form of great adhesiveness, and admirably 
fitted as a binding material in water-colour painting. 
Moreover, the various preparations of soluble starch 
possess in a high degree the property of becoming in- 
soluble in cold water after they have once become dry. 
In consequence, a pigment laid on in admixture with a 
soluble starch vehicle becomes, after it is dry, irremovable 
by water, so that further washes of colour may be added 
without disturbing the previous layers. 

U Soluble starch may be obtained by dissolving 10 
grams of caustic alkali in 400 cubic centimetres of water, 
and then stirring in 100 grams of starch previously ground 
into a paste with a little water. The mixture should then 
be carefully and uniformly warmed until it has become 
transparent. After heating for about fifteen minutes, 
hydrochloric acid is added to the paste until it no longer 



96 STARCH 

shows an acid reaction to litmus paper : the addition of 
a little ^-naphthol will protect the product from mould. 
Similar preparations of starch can be bought under 
various fancy names (such as vegetable glue). They are 
produced in the way just described, and are used in the 
preliminary priming of canvas instead of ordinary animal 
size ; but before the artist employs any of them, the sample 
should be tested with reddened litmus paper to see that 
it has no alkaline reaction, and with blue litmus to learn 
if an excess of acid be not present. For the careful and 
necessary neutralization of the product is not unfrequently 
omitted. 

The drawback to the preparation of soluble starch by 
treatment with caustic alkali lies in the presence of much 
alkaline chloride in the product ; it is not desirable to in- 
troduce sodium chloride, and still less potassium chloride, 
into a coloured drawing. An entirely satisfactory variety 
of soluble starch is obtained by the limited action of fresh 
malt-extract, in very small quantity, upon starch-paste 
at 75°. Or dilute sulphuric acid may be used, in the 
same way, to produce the desired transformation, the 
action being stopped directly the liquid becomes clear, 
by stirring in an excess of precipitated barium carbonate, 
which is subsequently removed by filtration. Still another 
method of preparing soluble starch is by heating it with 
glycerin. It is recommended to employ 6 grams of dry 
potato starch and loo grams of glycerin, heated together 
for about half an hour to 190° C, and then cooled down 
to 120** C. The soluble starch may be thrown down 
from this liquid by adding to it three times its bulk of 
strong alcohol. It must be remarked that the so-called 
* soluble starch ' prepared by the several methods just 
described is not precisely an identical product. In its 



HONEY 97 

most characteristic form it dissolves freely in hot water, 
but is deposited as a white powder during the cooling of 
the solution ; cold water holds about 3 per cent, in solu- 
tion. It is stated that the variety prepared by means of 
sodium peroxide is much more soluble in cold water. 

Starch contains carbon, hydrogen, and oxygen only, 
and is a carbohydrate having the empirical formula 
wCgHj^Og. It is a stable compound. Commercial starch 
always contains some water, generally from 12 to 18 per 
cent. 

Dextrin, or British gum, as met with in commerce, is 
prepared from starch in one or other of several different 
ways, and is a variable mixture of at least three varieties 
of true dextrin, soluble or modified starch, starch, a sugar 
called maltose, and certain minor ingredients and im- 
purities. It will suffice for the purpose now in view, if 
we select a commercial dextrin, free from acidity, dis- 
solving nearly completely in cold water, and then yielding 
a solution which, even when strong, has only a light 
yellowish or brownish colour. When a filtered cold-water 
solution of commercial dextrin is allowed to evaporate on 
a glass plate, and the residue becomes air-dry, the film 
of dextrin left differs from one of true gum by being less 
friable. A solution of dextrin is, however, far less ad 
hesive than one of true gum of the same strength. 

Honey now claims our attention. It is a common in- 
gredient in moist water-colours, and was often employed 
in size-painting. It is used to counteract the brittleness 
of gum or of size when dry, or, by its absorption and 
retention of water, to keep a paint moist. Honey con- 
sists of nearly equal quantities of two sugars known as 
dextrose and laevulose, a Httle sucrose or common sugar, 
small quantities of non-saccharine compounds, and about 

7 



98 GLYCERIN 

20 per cent, of water. As the useful properties of honey 
depend entirely upon its laevulose, a solution of this sugar 
should be employed instead of the raw honey : this may 
be easily prepared in the following way : Pure pale honey, 
kept until it has become crystalline and semi-solid from 
the separation of dextrose, is mixed gradually with four 
times its bulk of proof spirit, and thoroughly shaken at 
intervals for a few hours. The pale yellow alcoholic solu- 
tion is then filtered : the filtrate is a solution of laevulose, 
accompanied by small quantities of the other sugars of 
honey and of harmless impurities, and for some artistic 
urposes is at once available. Should it be desired to 
obtain a more concentrated solution of this substance, the 
liquid may be evaporated to the desired consistency in 
a porcelain basin, or it may be submitted to distillation 
in a retort. The aqueous solution of laevulose may be 
decolourized by filtration through warm animal charcoal. 

Laevulose, when free from water, forms a glassy solid ; 
but it is usually obtained as a thick syrup. Although 
this sugar is capable of assuming the crystalline form, it 
never does so under ordinary conditions. It has a strong 
attraction for moisture ; on this property its usefulness 
as a constituent of certain paints depends. 

Glycerin was discovered in 1779 by Scheele as a by- 
product in the preparation of lead-plaster ; for a long time 
the comparatively small quantity of glycerin met with in 
commerce was obtained in this way. It is now prepared 
from oils and fats by distilling them in a current of super- 
heated steam, sometimes by first saponifying them with 
alkalies, or decomposing them with sulphuric acid, and 
then submitting them to this distillation treatment. 

Glycerin generally occurs as a thick syrup with a sweet 
taste : when pure, it may be obtained in deliquescent 



GLYCERIN 



99 



crystals. Its empirical formula is CgHgOg. It is a 
strongly hygroscopic or water-attracting substance, the 
pure water-free glycerin being capable of absorbing more 
than one-third its weight of water from the air. Com- 
mercial glycerin ahvays contains water : the specific 
gravity of the liquid affords a rough method of estimating 
the amount. For pure glycerin at 15 '6° C. has the specific 
gravity 1*265, while that which contains 20 per cent, of 
water is reduced to i'2i3; with 30 per cent, it is i-i86, 
and with 40 per cent. i'i57. The presence of sugar, 
a not uncommon adulterant, may be recognised by the 
turbidity caused by mixing the glycerin, after evaporation 
to remove water, with chloroform. Glycerin containing 
lead darkens when sulphuretted-hydrogen water is added 
to it, while the presence of acids may be recognised by 
blue litmus-paper, which is not reddened by pure glycerin. 
The water-attracting property of glycerin induced me 
to use it as a substitute for honey in preparing moist 
water-colours so long ago as 1856, but I am given to 
understand that it was employed in 1847 by Messrs. 
Winsor and Newton. Even in cake-colours a trace of 
glycerin may be introduced with advantage, as it renders 
them less friable and more easily rubbed down with water. 
It prevents size, glue, and white of egg from becoming 
brittle on drying, and on this account may be used in the 
preparation of linen, canvas, etc., as painting-grounds. 
Care must, however, be taken in every case not to add 
more glycerin than is necessary to effect the purpose in 
view. It is a useful addition to gum-water, i dram to 
each ounce of gum present being sufficient ; some copying- 
inks contain it. Modelling clay may be kept moist by 
means of glycerin. 



CHAPTER IX 

WATER-GLASS, LIME- AND BARYTA-WATER 

The name water-glass appears to have been first applied 
to those silicates of potash and of soda which are soluble 
in water by Professor J. N. von Fuchs, in 1825; but 
Glauber, so early as 1648, made a soluble potash silicate, 
which he termed fluid silica. Van Helmont had prepared 
a similar compound in 1640- The actual manufacture on 
a commercial scale of these salts dates, however, from 
1825 only, and the credit of originating their production 
belongs to Von Fuchs. They differ from the compounds 
constituting ordinary and insoluble glass by containing 
no lime, baryta, alumina, or other earthy base. They 
are made in several ways. The purest sand obtainable 
is fused with carbonate of potash, or carbonate of soda, 
or a mixture in the desired proportions of these two car- 
bonates, in the presence of a little powdered charcoal. 
The fused mass dissolves by long continued boiling in 
water, and yields a heavy syrupy liquid of strongly alka- 
line reaction. By evaporating this liquid to dryness, and 
fusing the residue, the water-glass may be obtained in a 
solid form, and then closely resembles ordinary glass in 
appearance. Water-glass may also be made by heating 
flints red-hot, quenching them in water, and then digest- 
ing the powdered siHca thus obtained with soda-lye or 
potash-lye under pressure. 

100 



WATER-GLASS loi 

Three kinds of water-glass have been used in water- 
glass painting or stereochromy. One of these is a potash 
silicate, another is a soda silicate, the third is a mixture 
of these two, or a potash-soda silicate, called double water- 
glass. The solutions of the two former silicates as met 
with in commerce vary a good deal in their relative pro- 
portions of silica and alkali ; it is not desirable that they 
should contain so much silica as was recommended in 
the original papers of Von Fuchs, the inventor of stereo- 
chromy, and of Kuhlmann, who subsequently modified 
the process. Indeed, it has often been found useful to 
add a little pure caustic potash or caustic soda-solution 
or ammonia to the commercial solutions of water-glass 
before diluting them with distilled water for use in this 
process of painting. 

A solution of water-glass, if allowed to dry upon a piece 
of ordinary glass, leaves an opaque white irremovable 
stain. Water-glass alters or destroys, in virtue of its 
strong alkalinity, the great majority of organic pigments. 
On the same account it cannot be used with flake-white, 
aureolin, the chromates, vermilion, and several other 
mineral pigments. It hardens zinc-white, some of the 
ochres, earths, and terre verte, forming with them, or 
with some of their constituents, double silicates, which 
are quite insoluble in water. The fixative power of water- 
glass in stereochromy depends indeed mainly upon actions 
of this order which occur between it and ingredients of 
the plaster or painting-ground, and of the pigments. It 
was formerly supposed that when an alkaline silicate acted 
upon carbonate of lime a double decomposition occurred, 
of v/hich the only products were an alkaline carbonate, 
and lime silicate. But subsequent investigation has 
proved that the change in question is more complex, 



I02 LIME-WATER 

a considerable quantity of a double and insoluble silicate 
of lime and alkali being produced. Similar double silicates 
of potash or soda and zinc, of potash or soda and baryta, 
and of potash or soda and alumina, have been proved to 
exist in stereochromic work ; doubtless many others are 
also present. They are not only insoluble in water, but 
are harder than the materials out of which they have 
been formed. 

Commercial solutions of water-glass contain from 28 to 
60 per cent, of the alkaline silicate or silicates. They 
should be carefully preserved from access of air, the 
carbonic acid of which produces much alkaline carbonate 
(often separating in crystals in the case of soda), and finally 
causes the separation of gelatinous silica hydrates. The 
entrance of calcareous matters, gypsum, zinc-white, etc, 
should also be guarded against. 

The subject of water-glass is here treated very briefly, 
partly because the various processes of stereochromy, even 
with their latest improvements, are very little used in this 
country, and partly because the preparations of water- 
glass specially made for the use of painters may be trusted. 
To this latter observation I might add the remark that the 
problem of thoroughly examining a commercial water- 
glass solution for strength, purity, and due proportion of 
silica to alkali, is too complex to be undertaken except by 
a trained chemist. 

Lime-water is the name given to the solution in water 
of slaked lime, called in chemical language hydrate of lime, 
calcium hydrate, and calcium hydroxide. To prepare it, 
quicklime, which has been made by burning (as it is com- 
monly called) a pure marble, or, preferably, Iceland spar, 
is slaked with distilled water. The calcium hydrate formed 
is placed in a wide-mouth stoppered bottle, and covered 



LIME-WATER 103 

with several times its bulk of distilled water. The object 
of this treatment is to dissolve soda and some other soluble 
impurities, the major part of which will be removed when 
the watery liquid in the bottle is decanted from the un- 
dissolved excess of calcium hydrate which should then be 
again covered with distilled water which has been recently 
boiled. The stopper should be well ground and smeared 
with vaseline. The bottle should be shaken at intervals 
in order that the water may take up as much calcium 
hydrate as it can dissolve. After all, this amount is very 
small, not exceeding, at 15° C, 0*172 part by weight per 
hundred measures of lime-water. Thus a gallon of lime- 
water, saturated at about 60° F., could not contain more 
than 120 grains of calcium hydrate, corresponding to 
90 grains of pure lime or calcium oxide, CaO. In 
ordinary practice such a perfectly saturated solution is 
not attainable, while the most carefully prepared and 
strongest solution is sure to become weakened each time 
the stopper of the containing vessel is withdrawn by the 
removal of some of the lime in solution in the form of 
carbonate of lime. The clearest lime-water, from this 
cause and from its action on glass, always appears turbid 
after a time. 

Although so dilute a solution, lime-water gives the most 
marked reactions of an alkali : it turns red litmus paper 
blue, embrowns yellow turmeric paper, and imparts a 
crimson hue to colourless phenolphthalein paper. It acts 
energetically upon many organic and some inorganic 
pigments, owing to its alkaline or basic properties. The 
ease with which the Hme in lime-water unites with car- 
bonic acid, forming carbonate of lime ( = calcium car- 
bonate), and the bearing of this action, and of other 
properties of caustic lime upon the materials and 



104 BARYTA.WATER 

processes of painting are discussed in Chapters II. and 
XXIII. 

Baryta-water has its uses, but cannot replace lime-water 
in fresco-painting. It is a solution of hydrate of baryta, 
barium hydrate, barium hydroxide, for these names all 
belong to the compound, in distilled water. The distilled 
water used should have been recently boiled and then 
cooled out of contact with the carbonic acid of the air. 
The barium hydrate used may be purchased in the form 
of colourless crystals having the formula BaOgHg + 8 aq. 
These, if not sufficiently pure, may be washed with cold 
distilled water, or recrystallized from boiling water, in 
which they dissolve very abundantly. A saturated cold 
solution is made by placing rather more than i ounce of 
these crystals in a bottle containing a pint of distilled 
water : the bottle should be almost full, the stopper should 
be smeared with a little vaseline. If the crystals dissolve 
completely, after repeated agitation, a few more should 
be added so as to leave a small excess at the bottom of 
the bottle. If the solution be clear it may be used directly 
from the bottle, as required ; if filtration be needed, a 
glass plate should be placed on the funnel during the 
operation to prevent free access of air, and the clear filtrate 
should be received at once in the bottle in which it is 
to be preserved. A solution of barium hydrate saturated 
at 15° C, contains nearly 2*9 grams of BaO in 100 cubic 
centimetres, or 2,023 grains per gallon. It is thus about 
seventeen times stronger than a solution of calcium hydrate 
saturated at the same temperature. Baryta-water, as it 
is called, is a powerfully alkaline liquid, becoming covered 
with a film of white barium carbonate on exposure to the 
air. By blowing air from the lungs through a glass tube 
into baryta-water, a dense white precipitate is formed. 



BARYTA. WATER 105 

Unfortunately, the binding power of barium carbonate is 
almost nil, so that baryta-water in mural painting is of 
service, not directly as a medium, but for destroying 
traces of calcium sulphate (gypsum) in the plaster-ground, 
and thus liberating a corresponding amount of lime-water. 
It may also be used for testing the effect of an alkaline 
earth on the powdered pigments which it is proposed to 
use in the work, in order to see if they can withstand its 
action ; those unaffected by baryta will prove to be 
unchanged by Hme. 



CHAPTER X 

SOLVENTS AND DILUENTS 

The liquids to which attention is directed in the present 
chapter are, with very few exceptions, not miscible with 
water. Of water itself it is not necessary to say anything 
beyond this, that distilled water is best adapted for almost 
every purpose to which this liquid is applied in the prepara- 
tion of pigments, as a solvent for gum, honey, etc., and in 
the practice of painting in water-colours. Next to dis- 
tilled water may be ranked rain-water collected in the 
open country, then the softer kinds of water yielded by 
some streams, springs, and wells. Waters containing 
more than 20 or 30 grains per gallon of solid matters in 
solution should be avoided as far as possible. It should 
be noted that very hard waters tend to curdle or precipi- 
tate the particles of colouring matter in the water-colour 
paints which they may be used to dilute. 

Before considering the chief solvents and diluents, a 
list of the most important of those which have been ob- 
tained in a pure state or isolated may be given. Most of 
these are artificial or laboratory products, the natural 
liquids employed in the processes of painting being mix- 
tures, not infrequently both variable and complex. In 
the foUov/ing table the several definite compounds in- 
cluded are arranged according to their boiling-points, those 

106 



SOLVENTS 



[07 



which boil at low temperatures being placed first : an 
asterisk indicates that the liquid is miscible with water : 



TABLE 


OF SOLVENTS 




Name 


Boiling-point 


Specific 
Gravity 


Formula 


Ether - 


35°C.= 95° F. 


- 0719 - 


C.HioO. 


Carbon bisulphide 


46° 


= 115° 


- 1-271 - 


cs,. 


♦Acetone 


56° 


= 133° 


- 0798 - 


CsHeO. 


Chloroform - 


61° 


= 142° 


- I -500 - 


CHCI3. 


♦Wood-spirit - 


66° 


= 151° 


- 0798 - 


CH4O. 


♦Alcohol 


78° 


= 172° 


- 0794 - 


C^HgO. 


Benzene 


81° 


= 178° 


- 0-884 - 


CeHg. 


Toluene 


111° 


= 232° 


- 0869 - 


C.Hg. 


Epichlorhydrin 


117° 


= 243° 


- 1-191 - 


C3H5CIO. 


Perchlorethylene - 


121° 


= 250° 


- I -620 - 


CXI,. 


Amyl alcohol 


131° 


= 268° 


- 0-814 - 


C5H12O. 


Pinene - 


160° 


= 311° 


- 0-859 - 


CioHjfi. 


Cineol = eucalyptol 


173° 


= 343° 


- 0930 - 


CioH.sO. 


Cymene 


175° 


= 347° 


- 0-858 - 


C10H14. 


Sylvestrene - 


176° 


= 349° 


- 0-851 - 


CioHjg. 


Limonene 


177° 


= 351° 


- 0850 - 


^10^16. 


Dipentene 


177'' 


= 351° 


- 0846 - 


CioHi6- 


Citral - 


228° 


= 442° 


- 0-897 - 


C,oH,eO. 


Geraniol 


230° 


= 446° 


- 0-894 - 


C.oHasO. 



The pinene, sylvestrene, limonene, and dipentene named 
in the above table are examples of what are now called 
terpenes. Mixtures of these and of a few other terpenes 
of less importance constitute what is generally known as 
oil or spirit of turpentine. Terpenes are very frequent and 
often very abundant constituents of the volatile, ethereal, 
or essential oils extracted from plants. Some, however, 
of these volatile and strong-smelling essences consist 
mainly of liquids containing oxygen, such as cineol or 
eucalyptol, C^oH^gO, which occurs to a large extent in the 
oils distilled from many species of eucalyptus. Besides 
the compounds in our list and a certain number of essen- 



io8 ETHER 

tial oils from plants, we shall have to consider some of the 
more volatile liquid constituents of natural petroleum and 
of artificial paraffin oils. The fixed or fatty oils, which 
are constantly used in painting and in the manufacture of 
varnishes, have been already discussed in Chapter V. 

Ether, often called sulphuric ether, is a very mobile 
liquid of extreme volatility, and possesses a penetrating 
odour. Its vapour, given off" freely at ordinary tempera- 
tures, forms with air a highly inflammable and explosive 
mixture. Great care is therefore required in using this 
liquid ; no light must on any account be brought near it. 
It does not mix with water, but floats on the surface, 
although it dissolves in water to the extent of about lo per 
cent. Commercial ether contains water and alcohol along 
with traces of other impurities. It is seldom necessary to 
remove the alcohol from it (for varnish-making, etc.), but 
it can be got rid of by repeatedly shaking the crude ether 
with water, whereby much ether also is dissolved away. 
The water present interferes seriously with the use of 
ether as a solvent for resins, etc., but it may be removed 
by careful rectification with fused calcium chloride, that 
substance having previously been allowed to remain in 
contact with the liquid for a day. A final distillation 
from a little metallic sodium completes the drying of the 
ether and also removes, if used in sufficient quantity, the 
alcohol present. Great care is necessary in distilling 
ether to secure, by a current of ice-cold water in the 
condenser, the condensation of the vapour. 

Carbon Bisulphide. — This heavy, oily but volatile liquid 
readily gives off" vapour at ordinary temperatures. It is 
poisonous, and the same care in manipulating it must be 
taken as that insisted upon in the case of ether. The 
smell of the ordinary commercial bisulphide is most offen- 



ACETONE 109 

sive, but it is now possible to purchase a specially purified 
sort from which a particularly disagreeable sulphur-com- 
pound of nauseous odour has been removed. Carbon 
bisulphide sinks in water : it is a powerful solvent for 
many resins, and mixes perfectly with the fixed and 
essential oils in all proportions. 

Acetone also occurs in crude wood-naphtha. It has a 
penetrating but agreeable odour. It is miscible with 
water, alcohol, oils, etc., and dissolves many resins, 
camphor, fixed oils, and allied bodies. It is sometimes 
serviceable as a solvent for discoloured varnishes on 
pictures. Commercial acetone is very impure, containing 
wood-spirit, empyreumatic oils, and water. 

Chloroform is another powerful solvent of resins. It has 
a pungent but sweet taste, is not miscible with v/ater, and 
is very heavy. Commercial chloroform often contains 
alcohol and other foreign matters, from most of which it 
may be purified by redistillation from a little oil of vitriol 
followed by a second distillation from fragments of quick- 
lime. For making varnishes neither water nor alcohol 
should be present in chloroform, but there are other 
impurities which do not interfere with its employment 
for such a purpose. 

Wood-spirit, or methyl-alcohol, is a constituent of wood- 
naphtha, a product of the destructive distillation of wood. 
It rarely occurs in commerce in a state even approaching 
to that of purity. It is miscible with water in all propor- 
tions, but not with fixed oils. When free from water it 
may be used as a solvent for some resins, and for remov- 
ing discoloured varnish from oil-paintings. Methylated 
spirit now contains in 100 measures 9^ measures of crude 
wood-spirit and ^ measure of petroleum oil, the remainder 
being rectified spirit of wine. 



no ALCOHOL 

Alcoholy or pure spirit of wine, is met with in commerce 
practically free from all impurities save water. Proof 
spirit, rectified spirits of wine, and methylated spirit, 
though of service in cleaning oil-pictures and for many 
other purposes, ought not to be used in the preparation of 
varnishes. For this purpose pure alcohol, often called 
absolute alcohol, is required ; but provided that it con- 
tains no water the presence of wood-spirit is no drawback 
to its use. In commerce, nearly absolute alcohol, made 
both from spirits of wine and from methylated spirit, is 
obtainable ; but it may be prepared by operating upon 
the strongest available spirits of wine in the following 
manner : The spirit is distilled in a water-bath until no 
further strengthening of the alcoholic distillate is secured 
by repetition of the process ; then a dry retort is half- 
filled with small, clean, hard fragments of quicklime, the 
strong spirit is poured upon these so as to somewhat 
more than cover them, and then the whole is left over- 
night ; distillation from a water-bath is then commenced, 
when it will be found that a spirit comes over which con- 
tains no more than one part of water in two hundred. 
Even this small proportion may be removed by redistilling 
the alcohol from a very little metallic sodium. The last 
distillate, when a small portion of it is shaken up with its 
own bulk of benzene, should mix perfectly with the latter, 
causing no turbidity. But it should be borne in mind 
that absolute alcohol is a very hygroscopic liquid, greedily 
absorbing water from the air ; it must, therefore, be kept 
in well-stoppered bottles, filled almost completely. In 
absolute alcohol some of the more intractable resins, even 
some kinds of copal, readily dissolve. The specific gravity 
of absolute alcohol at 15^ C. is '794, while, if it contains 
but I per cent, of water, its specific gravity is distinctly 
higljer, namely, 797. 



BENZENE III 

Benzene is employed not only as a solvent, but as a 
diluent of the medium or oil employed in painting. It is 
obtained from the lighter naphtha separated in the frac- 
tional distillation of coal-tar. The benzene (also called 
benzol) of commerce is rarely pure. The presence of small 
quantities of higher hydrocarbons of the same series is of 
little moment, but it also contains about one half per cent, 
of a sulphur compound called thiophene (C^H^S), to which 
the offensive odour of ordinary benzene is partly due. 
Thiophene is, however, much more soluble in cold oil of 
vitriol than is benzene, and may be removed by several 
treatments of the benzene with small quantities of this 
powerful acid. Benzene thus purified can now be pur- 
chased. Benzene is a mobile liquid, not miscible with 
water, but dissolving readily in all proportions in most if 
not all of the liquids now being described. It dissolves 
oils and very many of the harder as well as all the softer 
resins. 

Toluene^ commercially known as toluol^ much resembles 
benzene, and may be used for the same purposes, although 
it is less volatile. Conunercial toluene has a disagreeable 
smell, arising from the presence of a sulphur compound 
(thiotolene), which is more difficult to remove from the 
liquid than the thiophene from benzene. 

Toluene of good quality and at a moderate price may 
be obtained from Kahlbaum of Berlin. It constitutes a 
useful diluent and solvent when used with the spirit-fresco 
medium. 

Epichlovhydyin has been employed as a solvent for some 
of the copals and other intractable resins in the manu- 
facture of varnishes. Without further trials it would be 
unwise to employ this liquid in artistic painting, yet the 
resins dissolved in it seem to retain much of their original 



112 TERPEN ES 

toughness and hardness. The same statement may be 
made in reference to several other similar chlorine com- 
pounds, which possess the merits of cheapness and non- 
inflammability. 

Amyl alcohol, the chief constituent of fusel-oil, is used 
by picture-cleaners for the removal of discoloured varnish. 
Its vapour is suffocating and even poisonous. 

Pinene, Sylvestrene, Limonene, and Dipentene, with several 
other similar compounds, are the main constituents of the 
various liquids to which the ordinary name of turpentine, 
or, rather, spirit or oil of turpentine, is applied. All these 
liquids are hydrocarbons, having the same composition in 
loo parts, expressed by the empirical formula Cj^H^g. 
But these liquids — of which about ten are known — differ 
from one another in some of their chemical and physical 
characters, such as oxidizability, boiling-point, specific 
gravity, and action on light. The extreme importance 
of turpentine in the process of oil-painting, and in the 
manufacture of varnishes, warrants a somewhat full con- 
sideration of its several constituents. 

Turpentine, properly so called, is not a liquid, but the 
solid or semi-solid resinous secretion of many trees, chiefly 
coniferous. Some exudes naturally, but much more is 
obtained by artificial incisions. It consists of a mixture 
of one or more true resins and resinous acids in which 
oxygen is present, with one or more liquid hydrocarbons 
which contain (as the name imports) nothing but carbon 
and hydrogen, and therefore no oxygen. These hydro- 
carbons are called in chemical language ferpenes, a term 
by which they will be designated henceforth in the present 
chapter. On distilling the crude turpentine or resins 
alone or with water, or in a current of steam, the terpenes 
distil over while the solid part remains behind ; this, on 



TERPEN ES 113 

fusion, is called rosin or colophony. It need not be 
further considered, as it is of no value in painting, being 
friable and more or less strongly coloured ; it is, however, 
employed in making certain ' dryers,' known as resinates 
(or better, rosinates), containing cobalt, manganese, etc. 
We confine our attention, therefore, to the distillate or 
terpenes. It should be added, however, that the leaves, 
cones, and other parts of many coniferous trees, them- 
selves yield various terpenes when submitted to distil- 
lation, and that many of the volatile or essential oils of 
aromatic plants other than conifers contain or consist of 
terpenes. The oils expressed from the rinds of lemons 
and oranges afford illustrations of this remark. 

Terpenes differ from one another in several obvious and 
in several obscure ways. Even now the chemistry of 
these liquids is not by any means clearly and completely 
unravelled. We need not here concern ourselves with 
those minute differences in chemical and physical pro- 
perties by which the identity of individual terpenes is 
established, but may confine our attention to their most 
salient characteristics. Of these none is more important 
than the behaviour of terpenes with regard to atmospheric 
oxygen. Some of these liquids absorb oxygen readily, 
and to a large extent, from the air, becoming thereby 
resinified — in fact, they thus yield sticky, resinous, semi- 
solid bodies, closely resembling the crude turpentine from 
which they have been prepared. Everyone who has had 
occasion to use spirit of turpentine frequently must have 
noticed the production of a sticky substance about the 
neck of the bottle in which this liquid has been kept. 
Moreover, the spirit of turpentine itself will often have 
been noticed to have become cloudy, viscid, or almost 
solid, especially if it has been contained in a bottle fre- 

8 



114 



TERPENES 



quently opened, and not quite full. Besides these obser- 
vations another will have been made — different specimens 
of spirit of turpentine will have been found to differ 
much as to the rate at which these changes have taken 
place. Some samples, even in half-full bottles, remain 
clear and limpid for long ; others become thick, opaque, 
and sticky in a few weeks. Such changes are undesirable 
•in a solvent, diluent, or painting medium, on many 
grounds. The resin formed is an unsatisfactory one — 
soft, sticky, and contractile. The liquid decreases so 
greatly in mobility, and increases so greatly in viscosity, 
that its utility in thinning oil pigments, and in making 
fine touches, is greatly impaired. And this thickening of 
the liquid is accompanied by the production of acid sub- 
stances and of water, which affect injuriously the ease of 
working and the stability of the picture. Spirit of tur- 
pentine should disappear by evaporation quickly and 
completely from the painting into which it has been intro- 
duced. Now, if it be easily oxidizable, even if it be kept 
from experiencing change before it is actually employed, 
it will, during the very time in which it is being used, 
attract oxygen; so that though a great part of it will 
escape by evaporation, the remainder will resinify on the 
canvas itself, adding a sticky deposit to the drying oils 
and hard resins which may have been used as the paint- 
ing medium. It is clear, from all the above considera- 
tions, that the greatest care ought to be taken in selecting, 
in the first instance, such a sort of spirit of turpentine 
as will resist oxidation under ordinary conditions. Even 
an inferior spirit may be used, with a minimum of dis- 
advantage, if immediately after distillation it be poured 
into a number of small bottles, so as to fill each of them 
completely ; they should be at once closed with sound 



TERPENES 



113 



corks. In this way the contents of a bottle may be used 
up very soon after it has been opened. Another precau- 
tion may be taken : A few small fragments of hard quick- 
lime may be placed in each bottle to absorb any moisture 
produced by oxidation, and also the acid bodies which are 
formed at the same time. Even with the choicer samples 
of spirit of turpentine, which pass much less easily into 
resins, this precaution is desirable ; but in this case the 
employment of many small bottles is unnecessary, and 
it will suffice to put a few hard pieces of lime, free from 
powder, into a pint or quart bottle, and then to fill it 
with the spirit. The clear liquid may be poured off as 
required for use, any disintegrated particles of lime sink- 
ing readily to the bottom of the vessel. 

Before giving details as to the sources and character- 
istics of the best terpenes, it may be useful to mention that 
commercial samples of spirit of turpentine m^ay be tested 
and compared by means of a very simple experiment. 
Obtain the required number of small flat-bottomed, conical 
glass flasks with wide mouths, one flask for each sample ; 
these flasks are known as Erlenmeyer's. Into the flasks 
pour enough of the several samples to cover the bottom 
to the depth of one-eighth of an inch ; label each flask 
to correspond with the sample, and lightly close each 
mouth with a plug of carded cotton — the date of the 
experiment should be added on the label. Shake each 
flask so as to cause a number of bubbles to be formed in 
the liquid ; the more rapidly these bubbles break, the 
better is the sample. Repeat the experiment of shaking 
the samples at short intervals for a few weeks — notable 
changes in the viscosity of the oils will be observed 
sooner or later. Any sample which after one month 
remains clear, and in which the bubbles formed on agita- 



ii6 TERPEN ES 

tion break almost as quickly as at first, may be accepted 
as of good quality. Another test for discriminating 
between the samples, so far as their state at the time of 
the experiment is concerned, is the very simple one of 
placing one drop of each oil upon a sheet of writing- 
paper, and gently warming the translucent stain it forms ; 
with a good oil the mark completely disappears. 

Two other obvious characteristics of different samples 
of spirit of turpentine may now be noticed — namely, 
odour and boiling-point. Some samples have a much more 
agreeable scent than others ; the vapour of these seems 
to have a less marked tendency to produce headache 
than that of the pungent and cruder-smelling varieties. 
The range in boiling-point is not very extensive ; but 
it may be taken as about 25° C, the figures ranging 
from 155' to i8i.° Samples having lower boiling-points 
evaporate more quickly than those which enter into 
ebullition at higher temperatures. The solvent power 
on resins differs with different kinds ; this is a property 
which is of importance in varnish-making, but very little 
accurate knowledge exists on this point. But there is one 
characteristic almost peculiar to the terpenes which must 
not be overlooked. When oxidizing they possess, unlike 
the alcohols and benzene and petroleum spirit, a power of 
starting or increasing the absorption of oxygen by linseed 
or other drying oils ; in fact, they act as siccatives. This 
property is constantly utilized in oil-painting ; probably it 
is connected with the formation of hydrogen peroxide which 
passes on its surplus atom of oxygen to the oil present. 

A few of the more important turpentine oils may now 
be named : 

American oil, chiefly from Finns palustris and P. 
Tceda. 



TERPEN ES 117 

Austrian oil, partly from Pinus Laricio, partly from 

P. Pumilio. 
Burmese oil, from Pinus Khasya. 
French oil, from Pinus Pinaster ( = P. marifima). 
German oil, from Pinus sylvestris, P. Cemhva, P. Abies, 

P. vulgaris, etc. 
Juniper oil, from Juniperus communis. 
Russian and Swedish oils, chiefly horn Pinus sylvestris 

and P. Ledebourii. 
Strasburg oil, from Abies pedinata. 

The above-named turpentine oils are accompanied by 
small amounts of various resins, camphor, and other 
oxygenated bodies, from which they may be separated 
by treatment with caustic potash, metallic sodium, and 
fractional distillation. 

From the above-named liquids a number of terpenes 
have been isolated. Among the better known of these 
the following may be mentioned. 

1. Pinene, with a boiling-point of 160° C. It exists in 
two forms, distinguished by their rotatory power on 
polarized light : dextro-pinene is the chief constituent 
of German and American oil of turpentine. The other 
form of pinene, laevo-pinene, occurs in large proportion in 
French oil of turpentine ; it absorbs oxygen less readily 
than dextro-pinene, and therefore resinifies more slowly. 
In consequence, it is more suitable for artistic uses, such 
as the thinning of paints, or as an ingredient of varnishes. 

2. Phellandrene. — Boiling-point 171° to 172°. This 
terpene has been separated from eucalyptus oil, that is, 
from the oil obtained by the distillation with water of 
the leaves of one of the numerous species of eucalyptus, 
E. amygdalina. It is one of the most alterable of all 
terpenes, and the oils containing it should be avoided. 



ti8 TERPENES 

3. Limone7te.-~ This terpene, like most of the others, 
occurs in two forms or varieties, having opposite actions 
on polarized light. It is sometimes called citrene. It 
boils at lyy*'. It is best prepared from orange-peel oil, 
which yields over 90 per cent, of dextro-limonene when 
distilled from caustic potash. When pure it is less alter- 
able than dextro-pinene and phellandrene, though it 
resinifies after a time. 

4. Sylvestrene. — Boiling-point 176°. When pure it has 
the smell of bergamot, but generally presents the odour 
of fir-wood. It is dextro-rotatory, and forms the chief 
constituent of Russian and Swedish oil of turpentine, 
and of some of the German oils. On exposure to air 
it oxidizes readily, and leaves a sticky resin. It has 
a particularly strong odour. 

5. Dipentene, which boils at about 177° C, is optically 
inactive, and may be made by heating some of the other 
terpenes to 250° — 270° for some hours, or by mixing 
dextro- and Isevo-limonene together. The only natural 
product in which dipentene is known to occur is the 
volatile oil which accompanies common camphor. Its 
odour resembles that of citron oil : it resinifies to about 
the same extent as limonene. 

From the preceding descriptions it may be gathered 
that of all the above terpenes, limonene and dipentene are 
the least alterable. They have, however, somewhat high 
boiling-points, and evaporate more slowly than most of 
the other terpenes. 

Here it may be mentioned that the presence of water 
in a terpene, or a mixed essential oil, may be detected by 
the cloudiness which it shows when mixed with thrice 
its volume of benzine or of petroleum-spirit. To remove 
traces of water from any of the less volatile liquids we 



TERPENES 



19 



have been considering, without having recourse to distil- 
lation from caustic potash, or from quicklime, the follow- 
ing simple procedure may be adopted : A glass flask is 
three-fourths filled with the liquid, and then it is kept at 
a temperature of 110° to 120° C, so that the moisture 
present is disengaged as vapour without the terpene or 
essential oil itself boiling : drops of moisture will condense 
in the neck of the flask, and may be removed from time to 
time by means of a roll of blotting-paper. The mouth of 
the flask should be loosely plugged with carded cotton. Of 
course this process is applicable only to liquids which boil 
at temperatures considerably over 120°, like the terpenes. 
In connexion with the terpenes two other liquids and 
one solid remain to be mentioned. The liquids are * oil of 
amber' and 'oil of copal.' These are obtained by strongly 
heating the resins in question. They are employed as 
efficient solvents for the harder resins. Oil of amber may 
be obtained in commerce at a moderate price. Its offen- 
sive smell, partly due to compounds of sulphur, may be 
lessened by adding to it some white lead and solid caustic 
potash, and afterwards distilUng it. It contains amongst 
other liquid constituents at least one terpene. Its boiling- 
point rises, as distillation proceeds, from 110° C. to 260°. 
Camphor is expressed by the formula C^gH^gO, and is 
obtained chiefly from Cinnamomum Camphora, a tree of 
Formosa, China and Japan. It is a tough crystalUne 
solid of penetrating odour and pungent taste. It is 
soluble in all the liquids named in the present chapter. 
Although it boils at so high a temperature as 204° C, it 
readily and rapidly volatilizes at ordinary temperatures. 
It is used to aid the solution of some of the harder resins 
in the making of varnishes, but its presence in a varnish 
is objectionable, for it slowly escapes after the apparen- 



I20 PETROLEUM-SPIRIT 

drying-up of the varnish, and thus causes a deterioration 
of the lustre and continuity of the resinous film. 

Petroleum -spirit. — When native petroleum and the 
similar materials obtained in the distillation of bitumin- 
ous shales, etc., are submitted to fractional distillation, 
the more volatile portions which come over first con- 
stitute the liquids variously known as benzine, gasoline, 
benzoline, ligroine, petroleum-naphtha, petroleum-ether, 
and petroleum-spirit. This liquid consists entirely of 
hydrocarbons, some of which belong to the paraffin series, 
while others are naphthenes. Their boiling-points are all 
under 170° C, while some of them boil as low as 50° ; 
indeed, commercial samples of petroleum-spirit often 
begin to enter into ebullition at a lower temperature even 
than this. The series of petroleum products may be 
roughly grouped thus : 

Petroleum-spirit boils below 170° C. ; specific gravity, 
•6 to 7. 

Lamp-oil, kerosene, photogen, or paraffin-oil, boils 
between 180° and 220°, and has a specific gravity of 78 
to -82. 

Solar-oil, lubricating-oil, vaseline, and paraffin-wax, are 
heavier products, with a range of specific gravity from 
•83 up to '94. Their viscosity increases with their density 
until the semi-solid vaseline and the solid paraffin-waxes 
are reached. The latter substances have been described 
already, the former are not available in painting : in fact, 
their presence even in traces in petroleum-spirit — an 
extremely useful solvent and diluent— should be carefully 
guarded against. They neither escape by evaporation 
nor harden in the lapse of time. Thus petroleum-spirit 
remains alone for further consideration. 

As a solvent for resins, and as an extremely volatile 



PETROLEUM -SPIRIT 121 

and very thin liquid for diluting oily vehicles and paints 
in the process of oil-painting, the variety of petroleum- 
spirit which boils between 50° and 70° C. is the most 
suitable. It contains hydrocarbons represented by the 
formulae CgHjg and CgH^^. It must be used with great 
caution on account of its easy inflammability and the 
readiness with which it gives off a vapour, which, when 
mingled with atmospheric air, is highly explosive. It 
may be used for many purposes in lieu of benzene (from 
coal-tar naphtha), being much cheaper and quite as 
efficient. A drop of this variety of petroleum - spirit 
on paper evaporates very quickly, leaving no greasy 
stain. 

Another variety of this petroleum-spirit is obtained 
by collecting apart the fractions which boil between 
100° C. and 130°. These contain heptane (C^H^g), octane 
(CgHjg), heptylene (C^H^J, and octylene (CgH^g), and 
other hydrocarbons. This mixture is less volatile than 
that just described, it dries more slowly, and is a less 
energetic solvent. 

A third variety boils between 130° and 170° and is avail- 
able for many of the purposes for which turpentine-oil is 
employed. It is not advisable, in my opinion, to use 
fractions having a higher boiling-point than 170° C. as 
additions to the pigments and vehicles of oil-painting, 
for, though their slow drying is sometimes an advantage, 
there exists the danger of their incomplete evaporation 
from the painted surface. If they remain even in traces 
in the finished work after it has been varnished, they may 
give rise to the same accidents as are caused by the 
treacherous though seductive asphaltum. 

It should be remembered that the various petroleum 
liquids just described do not resinify, nor do they leave 



122 OIL OF SPIKE LAVENDER 

any permanent stain or mark upon paper which has been 
moistened with them. 

In the Table of Solvents on p. 107 three liquids contain- 
ing oxygen and related to the terpenes find a place. Two 
of these, cineol or eucalyptol, and geraniol, represented by 
the empiric formula C^^H^gO, are alcoholic in consti- 
tution ; while the third, known as citval, belongs to the 
aldehydes. These and several other allied oxidized com- 
pounds, as well as a few ethereal salts known as esters^ 
enter largely into the composition of certain essential oils 
occasionally used in oil-painting. We will introduce a 
few remarks concerning some of these compounds under 
the names of the essential oils of which they are important 
components. 

Oil of Spike Lavender is obtained by distillation from the 
flowers of a species of lavender, Lavandula spica. Its 
specific gravity varies from -905 to "918 : it dissolves in 
three volumes of 70 per cent, alcohol. It contains about 
30 to 40 per cent, of an alcohol, linalol (C^QHigO), about 
5 per cent, of an ester, linalyl acetate, a considerable 
quantity of cineol (eucalyptol), and a small proportion 
of terpenes. It is often adulterated with rosemary oil. 
When spike oil is exposed for a long time to the air, the 
part which does not evaporate gradually thickens, owing 
to the oxidation of its constituents. This thickened oil, 
although usefully employed in the application to porcelain 
of enamel colours, is useless in oil and spirit-fresco 
painting. To preserve spike oil in its thin and mobile 
state, the precautions recommended in the case of tur- 
pentine (p. 114) should be taken. Spike oil is a powerful 
solvent of resins ; it is one of the components of Gambier- 
Parry's spirit-fresco medium. 

Oils of Eucalyptus are derived from many species of 



OIL OF ORANGE 123 

eucalyptus, and differ from one another widely as to the 
relative proportions in which their components exist, and 
also in their odour. Cineol, or eucalyptol, is the chief 
and most characteristic constituent of the majority of 
them, occurring to the extent of 50 to 65 per cent, in the 
oil from E. globulus, the commonest of all kinds. On the 
other hand, the oil from E. maculata^ var. citriodora, some- 
times contains no less than 95 per cent, of citronellal, an 
alcohol. This oil is of particularly agreeable odour, as 
are also the oils of E. cneorifolia, E. corymhosa, and E, 
dealhata. For a diluent in oil-painting it is probable that 
any one of these oils may be chosen with equal propriety, 
our choice being guided by the odour of the sample. 

Oil of Lemon. — Though the terpenes known as dextro- 
and laevo-limonene constitute the main portion of this oil, 
yet its characteristic odour is partly due to the presence 
of 6 to 9 per cent, of the aldehyde citral mentioned above. 
This compound is occasionally separated from lemon-oil ; 
by its removal the remainder becomes richer in terpenes 
and more fitted for the use of the painter. 

Oil of Orange. — This essential oil, which, like that of 
lemon, is obtained by expressing the rind of the fruit, is 
remarkably rich in limonene (dextro-limonene). This, 
with small quantities of other terpenes, makes up over 
95 per cent, of the oil. Although the expressed oil pos- 
sesses a yellow colour, it may be obtained absolutely free 
from colour and of agreeable odour, by distillation under 
reduced pressure. 

Oil of Rosemary. — This oil varies in specific gravity 
between -9 and '918. It contains about 20 per cent, of 
an ester, bornyl acetate (C^HgoOgi), and 6 per cent, of 
borneol. Its other constituents include lineol and two 
terpenes. 



124 CYMENE 

Cymene. — There are twenty or more varieties of the 
hydrocarbon expressed by the empirical formula C^qH^^. 
The best known of these is the agreeable lemon-scented 
liquid contained in cumin oil from the seeds of Cuniiniim 
cyminum. Its full scientific name is paramethylisopropyl- 
henzene, while its constitution is shown by the formula 
CH3.C6H4.CH(CH3)2. This hydrocarbon serves the 
same purpose as a diluent as the terpenes, but is too 
costly for general use. Doubtless some of the other 
forms of the C^qHj^^ hydrocarbon might be similarly em- 
ployed. The range of their boiling-points lies between 
1 68° and 204° C. Some are solid at ordinary temperatures. 



CHAPTER XI 

SICCATIVES OR DRYERS 

The terms ' siccatives ' and ' dryers ' are applied to three 
classes of substances. Perhaps the most correct or appro- 
priate application of these words is to those metallic com- 
pounds which are used in order to increase the rate at 
which the drying oils harden, but in the literature of the 
subject we often find that drying oils which have been 
thus treated, and likewise certain resinous solutions, are 
spoken of as siccatives. In the present chapter we describe 
the dryers proper only, referring our readers to the chapters 
on oils and on varnishes for the necessary particulars con- 
cerning the other materials which may be included in the 
group under discussion. 

Lead and several of its salts have been long and widely 
used as dryers. Metallic lead in the form of foil, litharge 
or lead protoxide, minium or red lead, lead peroxide, sugar 
of lead or lead acetate, the basic lead acetate, and white 
lead itself, have all been used in this way, chiefly for the 
purpose of making linseed or other painting oil dry more 
quickly. Some of these compounds, particularly sugar 
of lead, have been introduced into the very picture itself. 
It was a common practice to employ powdered sugar of 
lead or a solution of this salt in water to hasten the drying 
of vehicles and of slow-drying pigments which have been 

125 



126 MANGANESE DRYERS 

ground in oil. I have seen one of the results of this com- 
mingling of sugar of lead with the medium or the paint 
in the production of an immense number of small spots 
in the picture, sometimes appearing through the surface- 
varnish in the form of a white efflorescence. This 
efflorescence consists at first of lead acetate in crystals, 
but these soon attract carbonic acid from the air and 
become lead carbonate, which, in its turn, is changed 
into lead sulphide by the action of sulphuretted hydro- 
gen. This tendency of the lead compounds to yield 
brown or black lead sulphide is, indeed, the great draw- 
back to any use of these substances as dryers. When 
oil is left in contact with them, and especially when heat 
is applied to the mixture, some of the lead dissolves, 
forming, with the fatty acids of the oil, lead-soaps. These 
soaps are distributed uniformly throughout the oil, and 
help to make it dry and harden quickly. The same action 
occurs when white lead is ground as a paint with oil, and 
has been urged as an objection to the use of those white 
leads which contain hydrate of lead, a compound which 
acts upon oil more quickly and thoroughly than the car- 
bonate of lead. 

It will be seen, however, that while there may be 
reasons for permitting the use of a single lead pigment 
which possesses this peculiar property, there can be none 
for introducing into every part of a picture oils or other 
materials which contain a metal, like lead, so liable to 
cause discoloration and darkening, when other and per- 
fectly innocuous substances are available for producing 
the same siccative effects. On this account we omit 
further reference to the lead compounds, which have been 
and are still employed in the preparation of strongly- 
drying oils, etc., but pass on to the 



MANGANESE DRYERS 127 

Manganese compounds, of which the dioxide, the 
hydrated protoxide and sesquioxide, the borate, the 
oxalate, and the Hnoleate are the most important. 

Manganese dioxide, the black oxide, MnOg, is used in 
the form of a powder obtained by grinding the mineral 
pyrolusite. As the effectiveness of this compound is made 
complete only by the use of oil of vitriol, which needs 
subsequent neutralization with lime, it cannot be recom- 
mended as a material for rendering linseed oil intended 
for painting, or for making picture-varnish, more drying. 
The difficulty of preparing the manganese hydrates above 
mentioned constitutes an objection to their employment 
for this purpose. But the borate, the Hnoleate, and the 
oxalate of manganese may be obtained in commerce in a 
state of sufficient purity for our present purpose, and it is 
to them that we wish to direct attention. Borate of 
manganese may, moreover, be so easily prepared, that it 
is worth while to give here the necessary directions. 
One pound of pure manganese sulphate is dissolved in 
six pints of distilled water, the solution being filtered if 
cloudy. A few drops of the liquid are now to be tested 
with caustic soda solution — the precipitate formed should 
be white ; if it show a greenish, yellowish, or greyish hue, 
iron is probably present, and it will be necessary to treat 
the whole of the solution with caustic soda until a white 
precipitate falls, and then to filter it again. In order to 
produce manganese borate, a boiling saturated solution 
of pure borax is added to the manganese sulphate solu- 
tion until no more precipitate falls. The precipitate is 
collected on a filter and washed with hot distilled water 
until the wash-waters show no turbidity when a solution 
of barium chloride and a few drops of dilute hydrochloric 
acid are added to the last portion coming through the 



128 DRYERS 

paper. The borate of manganese is then dried in a warm 
place, and finally in the water-oven. One grain of it, 
warmed with linseed oil, is sufficient to render an ounce 
of the latter highly drying (see Chapter V.). The oxalate 
or the linoleate of manganese may be used in the same 
way, and there are also met with certain manganese 
* resinates ' which may be employed similarly. Cobalt 
resinate is also a powerful dryer. 

^ The quantities of lead or manganese compounds 
necessary to confer the drying character on oil are very 
small. With -2 to i 'o per cent, of the weight of the oil 
the maximum effect is so nearly attained that any further 
addition is unnecessary. If the manganese in the form 
of resinate or linoleate be dissolved in ten times its weight 
of turpentine, a siccative having very little colour but 
possessed of great power is obtained ; this, when added 
to the oil in the proportion of from i to 20, i to 50, or even 
I to 100, confers the drying character upon it without 
any further heating. Moreover, if this oil be allowed, 
under carefully adjusted conditions, to absorb enough 
additional oxygen for it to enter on the second period 
(p. 53), it dries with great rapidity. Oil of this kind, pre- 
pared with the smallest possible amount of a manganese 
salt, is much to be commended for the use of the artist, 
since it assures to the finished painting a longer life than 
any other preparation of this kind. 

Borate of lime and borate of zinc have been employed 
not only for rendering oils more quickly drying, but also 
in admixture with some of those oil-paints which dry with 
difficulty. Being colourless they are well adapted for 
use with white pigments, such as oxide of zinc. Several 
of the siccative materials sold under various fancy names 
consist of mixtures of these borates with carbonate of 



DRYERS 129 

zinc or oxide of zinc, manganese compounds being also 
sometimes added. Another dryer in common use is white 
vitriol or sulphate of zinc. Its siccative character is very 
slight. Most of the other siccatives employed by artists 
owe their efficacy to lead, or are resinous preparations. 
Siccatif de Courtrai is a very dangerous mixture, heavily 
loaded with compounds of lead ; Siccatif de Haarlem is 
a resinous preparation, which produces, on drying, a hard, 
brilliant, and tough film. This acquires, in course of 
time, a deep yellow hue, which, however, hardly affects 
the colour of the paints with which the siccative has been 
employed, because of the small proportion used. 

IF Here it may be mentioned that spirit of turpentine 
may be regarded as a fairly efficacious dryer, especially 
if the picture in which it has been employed is exposed 
to sunlight. This property of turpentine (terpenes) is 
not shared by the hydrocarbons of petroleum and of coal- 
naphtha, such as petroleum spirit, benzene, and toluene. 
This difference in chemical activity must be borne in 
mind if we would correctly estimate and foresee the 
results of employing these several liquids as vehicles or 
diluents. 

It may be well to remark in this place that many of 
the volatile solvents, described in this chapter, are danger- 
ously inflammable, and some are of a poisonous character. 



CHAPTER XII 

VARNISHES AND VEHICLES 

When an oil, such as linseed, walnut, or poppy, has been 

purified and made more quickly drying by one or other of 

the methods already described, it is often called 'varnish.' 

It has acquired the property of rapidly solidifying, when 

spread as a thin layer, into a tough transparent substance, 

endowed with a considerable degree of cohesiveness and 

elasticity, yet rather soft withal. Now oil of this character, 

although it has many uses in painting, is not quite hard 

enough for some of the purposes for which a true varnish 

may be required, but its defects may be amended by 

associating with it one or more of the resins described in 

Chapter VI. One class of varnishes is compounded in 

this manner of two materials, oil and resin, both of which 

are fixed or non-volatile. A second group of varnishes 

consists of a resin dissolved in a volatile solvent. And 

there are also mixed varnishes which contain at least three 

ingredients — namely, a drying oil, a volatile solvent, and a 

resin. As the varnishes which consist wholly of oil and 

resin are thick and intractable, it is usual to thin these 

according to the purpose for which they are intended, with 

varying amounts of some volatile liquid or solvent, spirit 

of turpentine being most frequently thus employed. In 

order to avoid too elaborate a classification, it will be 

130 



MASTIC VARNISH 131 

advisable to describe those varnishes which contain oil as 
oil or fat varnishes, and those which consist wholly of a 
resin and a volatile solvent as spirit varnishes. We de- 
scribe the latter first, as their manufacture is easier and 
their constitution simpler. In order to avoid repeated 
references to the descriptions already given of the several 
materials employed in making varnishes, it will be con- 
venient to state once for all that the oils used are described 
in Chapter V., the resins in Chapter VI., and the solvents 
in Chapter X. 

Mastic Varnish. — This is usually prepared by dissolving 
mastic in spirit of turpentine, although other volatile oils 
and even absolute alcohol may be employed. In order 
to prevent the mastic from agglutinating together, warm 
powdered glass, or warm fine white quartz sand, may be 
added to the resin before it is mixed with the solvent. The 
spirit of turpentine should be absolutely free from mois- 
ture, the mastic may be in tears, or, preferably, have been 
purified and dried as before directed. The materials are 
introduced into a capacious glass flask fitted with a cork, 
tube and condenser so arranged that, when the flask is 
heated in a water-bath, the vapours given off" from the 
solvent may be condensed and return to the vessel. The 
temperature of the water-bath may be 100° C. if oil of 
turpentine be used, but should not be allowed to rise 
beyond 78° C. if absolute alcohol or 96 per cent, alcohol 
(specific gravity '806) be substituted for the oil of turpen- 
tine. The following receipt gives a varnish which con- 
tains nearly 25 per cent, of its weight of mastic, but the 
proportion may easily be increased or diminished : 
14 ounces of mastic, 
44 „ „ spirit of turpentine, 
6 ,, ,, powdered glass, or fine sand. 



132 MASTIC VARNISH 

When the mastic has dissolved the varnish is allowed to 
cool, and then poured off into a closed glass vessel, in 
which it is allowed to rest until perfectly clear. Or it may 
be clarified by filtration through a plug of dried carded 
cotton fitted into a funnel. The funnel should be closely 
covered with a ground-glass plate, but a specially con- 
trived filtering apparatus has been designed for the pur- 
pose of preventing any escape of vapour during the pro- 
cess of filtration. 

The varnish prepared according to this receipt is nearly 
colourless, and leaves a brilliant glassy film when it evapo- 
rates on a smooth surface. But this film is very brittle, and 
easily abraded by gentle friction even with the finger, in 
fact it consists of little more than the original mastic resin, 
the fragility of which is well known. To obviate this 
brittleness many plans have been devised. Sometimes 
Venice turpentine, Canada balsam, or Elemi resin is 
introduced in small quantity, not exceeding one-seventh 
in weight of the mastic used. In consequence of such 
admixture of a natural soft turpentine the varnish pro- 
duced dries more slowly, and leaves a less brittle, tougher, 
more adhesive, and more elastic film on evaporation. 
Ultimately, however, these balsams become brittle like 
mastic itself. This remedy is, therefore, of a temporary 
character, but, at the same time, these additions do not 
interfere with the ease with which the varnish, when old 
and discoloured, can be removed from a painting by means 
of solvents or of friction, without injuring the glazing pig- 
ments which may lie immediately below it : they also 
render the varnish more easy of application. The other 
classes of substances added to toughen the resinous film 
left by the drying of a spirit varnish, are fixed oils, and 
those liquid paraffins which boil at temperatures above 



COPAL VARNISH 133 

170° C. A very small proportion of * manganese ' linseed 
oil is, perhaps, the more effective and safer toughener of 
the two, but its introduction involves the disadvantage 
just named. In many French mastic varnishes camphor 
is introduced for the same purpose to the extent of 5 to 
8 parts for each 100 of mastic. The camphor, however, 
gradually escapes by volatilization, the varnish losing its 
fine lustre and becoming brittle and fissured. It should 
be mentioned here that the more easily resinified varieties 
of oil of turpentine, when used as solvents for mastic, 
also toughen the resinous film left on the drying up of the 
varnish, although the effect is not permanent. If alcohol, 
benzene, light petroleum ether, or other non-oxidizable 
solvents be substituted for any kind of essence of turpen- 
tine in making mastic varnish, there is no doubt that the 
brilliant films they yield are more brittle and less adhesive. 

Sandarac and the various kinds of soft pale dammar may 
be substituted wholly or in part for the mastic mentioned 
in the receipt for spirit varnish above given. But if these 
dammars be used great care must be taken that they are 
themselves free from moisture, and that the oil of turpen- 
tine or other solvent be also perfectly dry. It has been 
recommended to employ oil of spike lavender instead of 
oil of turpentine in making mastic varnish. The spike 
oil in this case must be free from water, and freshly dis- 
tilled : mastic varnish thus prepared has less tendency to 
* bloom ' than the ordinary kind, but if pictures are var- 
nished in a perfectly dry atmosphere and kept therein 
till the surface has hardened, the formation of bloom is 
minimized if not prevented. 

A copal spirit varnish may be made by the use of 
acetone, or of ether (both water-free), or of absolute 
alcohol, light petroleum-ether, or benzene. The copal to 



134 COPAL VARNISH 

be dissolved may be either Sierra Leone copal, Zanzibar 
copal, or Demerara copal, the first two yielding the 
harder varnish, but the last-named being easier of solu- 
tion, or, rather, dissolving less incompletely. The pow- 
dered copal, prepared as directed previously (by exposure 
to the air, and heating), or first fused, or at least heated 
till it has lost from lo to 20 per cent, of its weight, is kept 
in contact with four times its bulk of the solvent until it 
is nearly dissolved. Three measures of dry oil of turpen- 
tine are then added, and the mixture submitted to distil- 
lation from a water-bath until three measures of the 
acetone or other original solvent have been drawn over : 
an efficient condenser must be used. If it be desired to 
prepare a mixed varnish (partly oil or fat varnish), 
I measure of 'manganese ' oil, and 2 measures of oil of 
turpentine may be used in lieu of the quantity of turpen- 
tine above mentioned, the distillation being then proceeded 
with as before. 

In another method of preparing copal (and amber) spirit 
varnishes the resins duly prepared and powdered are 
heated with the selected solvent under pressure — that is, at 
a temperature above that at which the particular solvent 
used boils under ordinary conditions. With purified oil 
of amber, oil of copal, oil of turpentine, oil of spike, or 
the heavier petroleum spirit, and on a small scale, glass 
tubes hermetically sealed and heated to 200° C. may be 
used, but if a higher temperature or more volatile solvents 
be employed, copper tubes with screw stoppers are 
necessary. But operations of this order can be carried out 
safely and successfully only in a well-equipped laboratory 
or factory by skilled operators, and it is therefore unneces- 
sary to furnish further particulars in a work like the 
present. 



COPAL VARNISH 135 

The preparation of fat or oil varnishes with the harder 
resins is generally attended with considerable difficulty; 
but there is as we have already mentioned, one way in 
which the difficulty may be lessened. By the aid of one of 
the powerful and very volatile solvents previously named, 
we prepare a spirit copal or amber varnish ; we then add 
the required amount of * manganese ' oil and draw off the 
volatile solvent by distillation, thinning the resinous solu- 
tion obtained with so much oil of turpentine as is necessary. 
If the copal or amber employed has been first roasted or 
fused, the varnish produced will be more or less dark in 
tint ; it is on this account that the exposure of the powdered 
resin to the air in a flat porcelain dish for seventy-two 
hours, at a temperature (of 220° C.) which does not cause 
discoloration, is recommended. But if, on the other hand, 
the copal or amber be merely powdered, some part of it, 
and that a considerable part, will probably remain undis- 
solved though swollen, and will therefore be wasted. The 
following process, in the main identical with one recom- 
mended in the American edition of Mr. Erwin Andres' 
work on varnishes, yields a pale and durable varnish when 
Sierra Leone copal or other hard copal is employed, and 
is doubtless well adapted for the preparation of amber 
varnish also. As will be seen, it is based upon the pre- 
liminary partial solution of the hard resin in chloroform, 
or in light petroleum spirit of about the same boiling- 
point. It may be stated at once that the proportions of 
the five ingredients used are approximately 10 parts by 
v/eight of copal or other hard resin ; 5 parts by weight 
of dried powdered glass or sand ; enough chloroform to 
cover the above substances ; 35 parts by weight of oil of 
turpentine, and 10 parts by weight of ' manganese' oil. 
The following is an outline only of the process. The 



136 COPAL VARNISH 

copal, after having been powdered and heated to 220° C. 
for seventy-two hours, is mixed with the glass or sand, 
and introduced into a retort ; chloroform in quantity 
sufficient to cover the mixture is added. After the lapse 
of twenty-four hours the dry oil of turpentine is poured 
in, and an upright condenser is attached to the retort. 
The retort is then heated to 50° or 60° C. for two hours, 
so that the chloroform continually returns to the mixture. 
Then the contents of the retort are allowed to cool, and 
the condenser slanted downwards to allow of the chloro- 
form being distilled over. This removal of the chloroform 
having been effected at a temperature so low that very 
little turpentine has come over, the remaining mixture in 
the retort is heated once more with the condenser in an 
upright position. The heat used must suffice to bring 
the oil of turpentine into vigorous ebullition — in an hour 
the whole of the copal should have dissolved. The ' man- 
ganese ' oil wanted should now be heated to 100° C, and 
then the copal mixture, when it has cooled to 70° C, 
added little by little to it with constant stirring, the tem- 
perature of the oil being maintained at 90° to 100°. When 
the mixture is complete the source of heat is withdrawn, 
but the varnish is still stirred for twenty minutes. Then 
it is allowed to settle, until quite clear, in glass bottles, 
or, if an appropriate filtering apparatus is available, it is 
filtered. In the latter case a little hot oil of turpentine 
may be used to extract any copal solution which may 
remain with the powdered glass or the sand in the retort. 
The older plan of preparing oil or fat varnishes with 
hard resins is still that usually adopted ; but it yields 
products which are darker in colour than those obtained 
by the method just described, as the copal or amber used 
has been previously heated or even fused, whereby it has 



COPAL VARNISH 137 

lost one quarter of its weight. One way of carrying out 
this plan consists in melting the copal in one vessel, and 
heating the oil until it commences to give off small bubbles 
in another ; then half the oil is poured in a very thin 
stream into the melted resin, and incorporated therewith 
by constant stirring. Complete union having been effected 
between the two materials, the mixture is incorporated 
with the remainder of the hot linseed oil, any portions 
adhering to the vessel being afterwards dissolved by means 
of oil of turpentine ; 30 parts of melted copal, 100 parts 
of linseed oil, and 70 parts of oil of turpentine, are pro- 
portions often employed in carrying out the process we 
are describing. This process may now be completed by 
adding to the solution of copal in linseed oil J of a part 
of manganese borate, stirring continually, and heating for 
two hours, or until the solution has acquired the character 
of a thick gold-coloured syrup which can be drawn out 
into threads. This point having been reached, the heating 
is discontinued, and the contents of the boiler allowed to 
cool to 60° or 70° C, and then is added the warm oil of 
turpentine which has been used to dissolve out any of the 
copal solution clinging to the vessel in which that resin 
was melted. Finally, the remainder of the oil of turpen- 
tine is very gradually introduced with constant stirring. 
Copal varnish prepared in the above manner ought to 
dry in twelve hours or sooner. It is scarcely necessary 
to say that this method of preparing varnish with copal 
or other hard resin is one that no inexperienced person 
should attempt ; not only is there some chance of partial 
or total failure, but there is serious risk of fire. An easier 
and less dangerous process requires a specially constructed 
heater, which is kept hot by a water-bath. Melted copal, 
copal or amber oil, * manganese ' oil, and oil of turpentine, 



138 COPAL VARNISH 

are the materials used. They are all introduced together, 
and, as the temperature during the process of cohobation 
does not exceed ioo°C., the time required is greater than 
in the previously described process. 

A good copal or amber varnish ought to leave a film 
(on a sheet of glass) which combines the qualities of hard- 
ness and toughness. The toughness is given by the oil, 
the hardness by the resin. Such a film should not become 
fissured even when it has been exposed to sunshine 
during a year. Much of the copal varnish of commerce 
is not made from true copal or anime at all, kowdi or 
kauri resin (from Dammava atcstvalis), which is much 
easier to dissolve, being employed instead — the product, 
however, is decidedly inferior. Sometimes several resins 
are mixed together in the preparation of a so called copal 
varnish. A guarantee of genuineness, in which the name 
or names and proportions of the resin or resins employed 
is inserted, should always be demanded when buying 
copal varnish. This ought to be furnished by the varnish- 
maker himself, for artists' colourmen rarely prepare oil- 
varnishes themselves. 

An ingenious process for rendering hard copals soluble 
in oil without roasting them in the ordinary way has 
been recently devised and patented by H. Terrisse. It is 
based upon the fact that the solid hydrocarbon, naphtha- 
lene, a by-product in the manufacture of coal-gas, shares 
with some other organic bodies, liquids as well as soUds, 
the property of dissolving hard resins when heated with 
them under pressure at a temperature not exceeding 
300° C. In this way the greater part of the loss in- 
curred when copals are roasted in the usual manner is 
avoided, while the discoloration of the torrefied resin does 
not occur. A mixture of i part of copal with 3 parts 
of naphthalene is taken, and then heated for an hour or 



MEDIUMS FOR OIL-PAINTING 139 

two until complete solution has been effected. The mass 
is then transferred to a suitable still, when the naphtha- 
lene, being volatile, along with a little moisture and some 
oil of copal separated in the operation, are distilled off. 
Subsequent operations are two — the incorporation, under 
pressure, with the altered copal of the necessary propor- 
tion of linseed oil ; and, secondly, the addition of spirit 
of turpentine to thin the product, which is pale in colour 
and yields a sound varnish. Hard copals treated by this 
process suffer changes less profound than those brought 
about by the higher temperature involved in roasting 
them ; they consequently retain more of their original 
qualities of hardness and toughness when finally turned 
into varnishes. 

For the general use of painters in oil nothing more is 
wanted than true copal or amber oil-varnish, a drying oil, 
and a diluent. Of these three liquids a mixed medium in 
general use is compounded by taking equal measures of 
the three — varnish, oil, spirit of turpentine — and mixing 
them together in small quantities as required. But con- 
sidering the large quantity of oil already associated with 
oil-pigments and present in copal or amber oil-varnish, 
one-third of oil in the medium seems a somewhat high 
proportion. I have proved by numberless experiments 
that it may be reduced with perfect safety to the perma- 
nence of the picture, although the manipulation and 
technique of a painter may demand the peculiar quality 
in a medium which oil in considerable proportion can 
alone supply. A formula which answers well is this : 

2 measures of copal oil-varnish made from Sierra Leone 
or Zanzibar copal ; 

1 measure of poppy oil ; 

2 measures of oil of turpentine or oil of spike. 



I40 MEDIUMS FOR OIL-PAINTING 

By substituting linseed oil for the poppy oil a more 
quickly-drying medium is obtained ; still more rapid 
drying is secured by means of ' manganese ' oil. With 
the same object in view, benzene may be used instead 
of oil of turpentine. This latter ought, of course, in 
all cases, to be one of the least resinifiable varieties 
obtainable. 

If an amber or copal varnish containing no oil be 
available, a good medium may be prepared by mixing 
3 measures of it with 2 measures of poppy or linseed oil, 
and I measure of oil of turpentine or of spike. 

Bell's medium contains no resin, but consists of thick- 
ened linseed oil dissolved in oil of spike. To prepare it, 
pure linseed oil may be oxidized by having a current of 
warm, moist air passed through it until it has acquired 
the consistence of fresh honey : this change occurs slowly 
when a layer of oil is exposed to the air in a large flask, 
the mouth of which is lightly plugged with carded cotton. 
The flask should be shaken occasionally to mix its 
contents, and to prevent the formation of a pellicle on 
the surface of the oil. 

Paintings executed with this thickened oil medium do 
not acquire the hardness and solidity of those carried out 
with a vehicle containing a hard resin. 

Roberson's medium has now been in use for something 
like seventy years. It has been and is a favourite vehicle 
with many distinguished artists. A substitute for it is 
sometimes prepared in the studio by mixing and warming 
together strong copal varnish, poppy oil or linseed oil 
and a trace of white wax. 

Of megilp — a mixture of linseed oil and mastic varnish 
— it is only necessary to say this : that however agreeable 
as a medium with which to work, it contains a poor and 



MEDIUMS FOR OIL-PAINTING 141 

weak resin, which becomes in course of time yellow and 
brittle, and is liable to be injuriously affected when a 
picture, in which it has been used freely, is cleaned. 

For painting in oil on plaster, slate, or stone, a perfectly 
sound and convenient medium is made by warming 12 
ounces of oil of spike, or of non-resinifiable oil of turpen- 
tine in a glass flask plunged in water heated to the boiling- 
point, and then pouring into it in a slender stream 4 ounces 
by weight of paraffin-wax (melting-point about 58° to 
62** C), or of ceresin, or of a mixture of these materials. 
The mixture becomes perfectly clear if it be thoroughly 
agitated and maintained at a temperature of 80° C. Then 
20 measured ounces of ' picture '-copal varnish, or 16 
ounces of oil-copal varnish, are slowly added, with con- 
stant shaking, in the same way. It is of the highest 
importance that the copal varnish used should contain a 
sufficiency of oil. If a thin varnish with much terpene 
be employed in preparing this medium the pigments may 
lack coherence. I have found this defect counteracted 
by using pigments ground in inspissated or blown linseed 
oil, rather than in the medium itself. The * paraffin- 
copal ' medium thus obtained may be diluted with oil of 
turpentine exactly to the same extent as recommended 
by the late Mr. Gambler- Parry, in the case of his ' spirit- 
fresco ' medium, and may be used in the same way and for 
the same purpose. Paintings executed with this medium 
present a perfectly dead or matt surface without the least 
shine. This medium is superior to that used in spirit- 
fresco, for it contains neither elemi-resin nor wax, the 
two doubtful constituents of the latter preparation, but it 
is not so pleasant in use. Moreover, if a painting executed 
with this medium on canvas be rolled up, the paint seems 
to have some tendency to crack. This accident may be 



142 SPIRIT-FRESCO MEDIUM 

obviated if the rolling up and the unrolling afterwards 
be carried out in a warm room. 

Mr. Gambier-Parry's medium, to which reference has 
just been made, is prepared with five ingredients. The 
original instructions are unnecessarily complicated, and 
may be simplified while keeping to the original propor- 
tions, and without modifying the nature of the product 
in the slightest degree. Eight ounces of oil of spike are 
warmed in a glass flask to 80^ C, then 2 ounces by weight 
of elemi are added, the mixture being warmed and shaken 
till the elemi has dissolved. Some dirt and woody frag- 
ments are sure to be introduced with the elemi, and so 
the solution (still warm) must be filtered. Upon the filter, 
when all the liquid has run through, 2 ounces by measure 
of oil of turpentine, heated to 80° C, are now poured, and 
the united filtrates are thoroughly mixed. The liquid is 
then introduced into a flask, and heated to 80° C. ; then 
4 ounces by weight of pure white wax (previously melted) 
are poured in a thin stream into the solution of elemi and 
thoroughly shaken. When the commixture is complete, 
20 ounces by measure of ' picture '-copal varnish, or 16 
ounces of oil-copal varnish, are gradually introduced with 
constant agitation. The water surrounding the flask is 
now made to boil, and kept boiling for five minutes. The 
flask is withdrawn, wiped dry, and allowed to cool. As 
the cooling proceeds the flask is gently- agitated from 
time to time. When the mixture begins to get treacly in 
consistence it is at once poured into the bottles (bottles 
with wide mouths, holding 4 ounces apiece, are con- 
venient) in which it is intended to preserve the medium 
for use. The dilution of this medium and the mode of 
using it are described in Chapter XXIII. on Painting 
Methods. 



PART III 
PIGMENTS 

Chapter XIII.— White Pigments Chapter XIV.— Yellow Pigments. 
Chapter XV.— Red Pigments. Chapter XVI. - Green Pigments. 
Chapter XVII.— Blue Pigments. Chapter XVIII.— Brown Pig- 
ments. Chapter XIX. — Black Pigments. Chapter XX. — Classifi- 
cation of Pigments. Chapter XXI. — Tables of Permanent and 
Fugitive Pigments. Chapter XXII. — Selected and Restricted 
Palettes. 



CHAPTER XIII 

WHITE PIGMENTS 

Flake-White: White Lead — Ceruse — Blanc d* Argent — 
Blanc de Plonih — Bleiweiss — Kremsevweiss. 

White lead was known to the ancients. A face-powder 
or cosmetic, found, in its original pottery-box of about 
400 B.C., in the neighbourhood of Athens, proved to be a 
mixture of white lead and whitening. Theophrastus, 
Pliny, and Vitruvius describe its manufacture from lead 
and vinegar. It was designated by several names, such as 
cerusa, cerussa, cerosa, psimuthion. In the first half of 
the fourteenth century it is mentioned as ' minium album.' 
It has been called by divers names after the place or 
method of its manufacture, or after persons who have 
devised special processes for preparing it. 

White lead still continues to be made for the most part 
by processes which are essentially identical with the old 
method, now generally known as the ' Dutch ' process. 
This consists in attacking metallic lead, in the form of 
'crates,' 'grids,' or spirals, simultaneously by acetic acid, 
carbonic acid, atmospheric oxygen, and water-vapour. 
The metal is gradually converted into a mixture or com- 
pound of lead carbonate and lead hydrate. Other pro- 
cesses, generally yielding an inferior product, containing 
more carbonate and less hydrate, have been used. One 

145 'o 



146 FLAKE-WHITE 

of these consists in passing a current of carbonic acid gas 
through a solution of lead subacetate ; in another, 4 parts 
of litharge, i part of common salt, and 16 parts of water, 
are kept in contact for some hours with constant agita- 
tion, and then carbonic acid gas is led into the mixture 
until it becomes neutral to test-papers. 

The best white lead contains two molecules of lead car- 
bonate intimately associated with one molecule of lead hy- 
drate, and is represented by the formula 2PbC03,PbH202- 
This formula corresponds to about 70 per cent, of lead 
carbonate, and 30 per cent, of lead hydrate. If the pro- 
portion of hydrate rise above this percentage, the opacity 
of the paint is lessened seriously ; if it fall much below 
the above-named figure, the binding-power and working 
quality of the white lead are impaired. Although the 
normal lead hydrato-carbonate is probably constituted of 
one molecule of each of its components, the formula 
previously given may be taken to represent the highest 
quality of white lead as a paint. It has been recently 
stated that two molecules of lead hydrate associated with 
three molecules of barium carbonate constitute a pigment 
actually better than flake-white in some respects. 

It is scarcely necessary to say that the metallic lead 
used in the manufacture should be as nearly pure as 
possible, such, for instance, as the lead from the Upper 
Hartz, which contains but 2 parts of foreign metals per 
1,000. These foreign metals, the presence of any one of 
which in sensible quantity may cause a discoloration of 
the product, are copper, bismuth, silver, cadmium, anti- 
mony, nickel, and, more particularly, iron. But not only 
must the raw material be pure, but it is necessary to 
guard against the contamination of the white lead, during 
its manufacture, by dust or sulphuretted gases. 



WHITE LEAD 



147 



The impurities and defects of white lead are (i) acci- 
dental, (2) intentional. 

(i) Of the accidental impurities and defects of white 
lead made from pure metal, the following are the chief: 

a. Metallic lead, imparting a grey hue to the pro- 

duct. 

b. Massicot or litharge, the yellow oxide of lead. 

c. Minium or red lead, which gives a rosy hue. 

d. Excess of lead hydrate, which causes translucency. 

e. Excess of lead carbonate. 
/. Lead acetate. 

A simple experiment will suffice to show whether lead 
acetate be present in objectionable proportion in any 
sample. Some of the dry pigment is to be ground with 
distilled water into a paste, thrown on to a wetted filter 
and then washed with freshly-boiled distilled water. The 
clear filtered liquid should give nothing more than a slight 
cloudiness on the addition of a little dilute sulphuric acid. 
Some samples of flake-white which had been insufficiently 
washed contained from 2 to 1 1 per cent, of lead acetate 
removable by distilled water. In order to ascertain 
whether the lead carbonate and lead hydrate exist in due 
proportion in a sample of white lead, a weighed portion 
of the dry pigment, after having been dried at 212° F., 
should be carefully roasted in a current of dry air, and 
the water evolved (2 to 3 per cent.) intercepted by means 
of a weighed calcium chloride absorption tube. This 
operation, however, requires much manipulative experi- 
ence, and, unless accurately performed, may lead to 
erroneous conclusions. 

(2) Of the intentional adulterations of white lead the 
following are the most usual : 



148 WHITE LEAD 

a. Heavy spar, that is, native barium sulphate ; or 

the same compound artificially prepared (per- 
manent white, blanc fixe). 

b. Gypsum. 

c. China-clay. 

d. Whitening or chalk. 

e. Lead sulphate. 

The first of these adulterations is by far the most usual. 
Barium sulphate, in the form of finely -ground barytes, or 
heavy spar, is the material employed on the large scale 
for cheapening the cost of production of ordinary white 
lead ; precipitated, that is, artificially prepared, barium 
sulphate is used in the case of the finer makes of this pig- 
ment. In either case the sophistication is very readily 
recognised. Pure flake- white, for example, loses 14 J per 
cent, of its weight when strongly heated so as to drive off 
its carbonic acid and water, but * Venice ' white, which 
is white lead and barium sulphate mixed in the proportion 
of equal parts, loses, under such treatment, no more than 
7*3 grains per 100. ' Hamburg' white, with 33 per cent, 
only of white lead, loses 4*8 per cent., and ' Dutch ' white, 
of which three-fourths are barium sulphate, gives off no 
more than 3*8 per cent. * Crems,' or ' Cremnitz ' white, 
is, or ought to be, pure white lead. The complete solu- 
bility of pure white lead in dilute nitric acid may also be 
made use of to detect the presence of barium sulphate, 
which will remain undissolved as a dense white powder. 
The adulterations with gypsum, china-clay, whitening and 
lead sulphate, can be recognised only by further tests. 
Gypsum, for instance, gives off water when heated, and 
I part of it dissolves in 420 parts of water. China-clay 
also gives off water when heated, but is insoluble in 
water, and only slightly soluble in nitric acid. Whiten- 



WHITE LEAD 149 

ing dissolves in all mineral acids, but lead sulphate is 
practically insoluble. After all, the detection of barium 
sulphate is the only point with which the painter need 
concern himself. It will therefore suffice if he ascertain 
that a sample of white lead is of first-rate colour and 
body, contains no sensible quantity of lead acetate, loses 
when heated 14 J per cent, of its weight, and dissolves 
perfectly in dilute nitric acid. 

It has been observed that white lead is less liable to be 
blackened by sulphuretted hydrogen and by other sul- 
phides when it contains a small quantity of baryta-white, 
or of lead sulphate thoroughly incorporated with it by 
grinding. This observation opens the door to adultera- 
tion, it is true : and it is perhaps wiser to rely upon the 
protection furnished by resinous mediums and a final 
coat of mastic varnish rather than upon any admixture 
with other white substances. 

The drawbacks attendant upon the use of white lead as 
a paint are its poisonous character, its sickly and noxious 
smell when used with oil, and its liability to discolour when 
exposed to sulphuretted hydrogen or any sulphide soluble 
in water. On the other hand the quality of the whiteness 
of the best flake-white is unimpeachable: the paint works 
admirably in oil, and has great body ; moreover, flake- 
white not only mixes perfectly and safely with the majority 
of permanent pigments, but it serves to impart to slow- 
drying colours its own strongly siccative character. 
Besides all these merits white lead possesses a valuable 
property, which has scarcely been clearly recognised or 
duly appreciated. For when an old oil-picture is carefully 
examined, it will generally be found that if any portion of 
its surface (of the paint, not the varnish) show decided 
contractions and cracks, these are precisely those portions 



150 . WHITE LEAD 

into which white lead has entered in smallest proportion, if 
at all. The most translucent parts, the rich glazings and 
the deepest shadows may be fissured, but not the high 
lights : examples illustrative of this point are referred to 
in Chapter XXIV. of the present volume. This property 
of white lead seems to depend upon a combination taking 
place between a part of the oil with which it is ground and 
a part of the lead hydrate which it contains. A degree of 
toughness and elasticity is thus imparted to those films 
of oil paint into which lead-white enters to any consider- 
able extent. 

Flake-white becomes brown, grey or black when ex- 
posed to the action of sulphuretted hydrogen, ammonium 
sulphide, or any metallic sulphide soluble in water. This 
discoloration, which is due to the formation of lead sul- 
phide, occurs more readily in the presence of moisture : 
it is favoured by darkness to such an extent that a piece 
of perforated cardboard laid upon a dry oil-painted 
surface of white lead will, after a few weeks' exposure, 
give a white pattern representing the perforations on a 
buff ground, which corresponds to the solid parts of the 
cardboard. But, after the removal of the perforated 
card and subsequent exposure of the painted surface to 
strong light, this pattern will disappear, the coloured 
sulphide of lead being oxidized into the white sulphate. 
The same change may be more speedily brought about 
by means of a solution of hydrogen peroxide. By laying 
a sheet of white filter-paper soaked in this liquid upon the 
discoloured lead-priming of a prepared canvas the original 
colour of the paint may be gradually brought back, 
especially by the aid of a moderate degree of warmth. 
This method is not available in the case of drawings or 
water-colour paintings in which flake-white has black- 



LEAD SULPHATE 151 

ened ; but even these may often be successfully treated 
by exposure to moist ozone, or by light touches of a 
solution of hydrogen peroxide in ether. The latter treat- 
ment has been successfully applied to a series of archi- 
tectural drawings in gouache by C. Clerisseau in the Soane 
Museum. In these the high lights had become black. 
Old silver-point drawings, in which the lights were height- 
ened with lead-white, may sometimes be thus restored to 
their pristine state. 

The specific gravity of the best flake- white is 6*6 ; 100 
parts by weight of it require from 11 to 15 parts of linseed 
oil in order to form an oil-paint of suitable consistence. It 
is sometimes ground with poppy oil when a particularly 
pure white product is demanded. The yellowish tint of 
some makes of white lead is occasionally neutralized by the 
addition of a trace of indigo or of artificial ultramarine. 
Burnt or roasted white lead is sometimes used as a pig- 
ment. It is of a cream-colour, a buff, or a pale yellowish 
salmon, according to the temperature at which it has 
been prepared, or the length of time during which it has 
been heated. 

Lead Sulphate. — Many attempts have been made to 
utilize the sulphate of lead (PbSO^) as a pigment. This 
compound, which is nearly insoluble in water and in dilute 
acids, is almost, if not entirely, destitute of poisonous pro- 
perties owing to this insolubility, although as ordinarily 
prepared it possesses neither the pure whiteness nor the 
body of white lead. But under the name of Freeman's 
white lead, or non-poisonous white lead, a paint has been 
introduced which may prove a rival to ordinary white 
lead. It is essentially lead sulphate, and is prepared by 
precipitating lead acetate solution with sulphuric acid. 
But this precipitate is subjected to a special process of 



152 ZINC- WHITE 

grinding with small quantities of zinc-white and barium 
sulphate, and acquires thereby a considerable increase of 
density and opacity, although both the latter compounds 
are of less specific gravity than the lead sulphate to which 
they have been added. Being, when ground in oil, not 
only destitute of the disagreeable smell of white lead, but 
much less readily darkened by sulphuretted hydrogen. 
Freeman's white possesses distinct advantages in these 
respects over the more common paint. It may be mixed 
with other permanent pigments without injuring them : 
it is practically non-poisonous. On the other hand, it 
does not possess the remarkable hardening and drying 
powers of white lead. 

Lead Oxychlovide. — Pattinson's white (PbClHO) does 
not possess any advantage, as a white pigment for artists' 
use, over the ordinary flake-white. Similar verdicts may 
be pronounced as to the eligibility of several other white 
compounds of lead, such as the antimonite, the anti- 
moniate, and the tungstate of this metal. 

The blanc d'argent of the French is supposed to be 
pure lead carbonate free from any hydrate, but the great 
majority of the specimens which I have examined are 
nothing but flake-white of good quality. For general use 
as a white pigment, both alone and in admixture, the best 
flake-white, with all its defects, presents distinct advant- 
ages over pure lead carbonate free from lead hydrate. 

Zinc-white : Chinese white — Blanc de Zinc — Zinkweiss. 

The substitution of carbonate of zinc for white lead 
seems to have been first suggested by Courtois of Dijon 
in 1787. After several unsuccessful attempts to introduce 
either the carbonate or the oxide as an oil paint, the latter 
began to be used about 1849-50, shortly after Leclairehad 



ZINC-WHITE 153 

shown how to prepare an oil suitable for making the paint 
dry. We believe that it had been frequently employed as a 
water-colour many years before 1849. So early as 1834 
Messrs. Winsor and Newton prepared a peculiarly dense 
form of this pigment under the name of Chinese white. 

For the preparation of the best zinc-white it is essential 
that the zinc be pure ; especially should it be as free as 
possible from the metal cadmium. The zinc is heated to 
the distilling-point in crucibles or retorts set in a furnace ; 
the vapour, meeting with air, burns into the white oxide, 
which condenses in a series of chambers. The contents 
of these chambers vary somewhat in purity of tint ; the 
presence of some metallic zinc generally imparts a greyish 
hue to the zinc oxide nearest the crucibles or retorts. By 
selecting the densest and whitest product, and then sub- 
mitting this to powerful mechanical compression when 
red-hot, an excellent pigment having a dense body is 
obtained. Zinc-white prepared in the wet way, as by 
the action of lime-water upon zinc chloride, is inferior in 
substance to that made as above described, while that 
obtained directly from blende is of bad colour. 

As an oil-paint, zinc-white is a bad dryer. Instead of 
being ground in raw poppy or linseed oil, an oil rendered 
highly siccative by borate of manganese should be em- 
ployed. In spite of its unquestionable merits, zinc-white 
in oil cannot be recommended as a complete substitute for 
flake-white. When used freely, it often shows a tendency 
to crack and scale, besides becoming with age more trans- 
lucent, or rather, less opaque. For water-colour painting, 
tempera, and for fresco, zinc-white is practically perfect, 
being unchangeable in hue or opacity under the most 
adverse influences. Paper washed with zinc-white, either 
alone or tinted with a coloured pigment, affords a good 



154 BARYTA-WHITE 

ground for silver-point, platinum-point, or pencil draw- 
ings. There is a peculiar 'tooth' in the zinc-white which 
freely brings off the metal or graphite from the pencil} 
and serves to fix it on the prepared surface. 

The purity of zinc-white is easily tested. Heated in a 
tube, it should yield no volatile product, and should suffer 
no permanent change of hue. It should dissolve com- 
pletely without effervescence in boiHng dilute nitric or 
hydrochloric acid. If, on heating, it acquires a permanent 
yellowish hue, giving off moisture at the same time, white 
lead is probably present. If it does not dissolve completely 
in acid, it probably contains barium sulphate ; if efferves- 
cence occurs during solution, either whitening, or white 
lead, or zinc carbonate is present. Zinc carbonate, however 
prepared, is inferior in whiteness and body to the oxide. 

Zinc sulphide has been prepared as a paint ; its liability 
to evolve sulphuretted hydrogen renders its use as an 
artists' pigment dangerous, for there are several other 
colours upon which it would exert a deleterious action. 
It has very considerable body. 

Baryta-white ; Permanent white — Blanc Fixe — Permanent 

Weiss. 

The mineral known as heavy spar, or barytes, has been 
used as a white paint, particularly as an adulterant for 
white lead. However finely it may be ground, it is always 
very inferior in body and covering-power to the artificially- 
prepared barium sulphate — the true blanc fixe. To make 
this, a cold solution of barium chloride of specific gravity 
I* 19 is prepared, and to it is gradually added in the cold, 
and until no further precipitate is formed, dilute sulphuric 
acid of 1*245 specific gravity. The barium sulphate is 



MINOR WHITE PIGMENTS 155 

washed with cold water until the wash-waters are entirely 
free from acid ; for many purposes to which the product 
is applicable (fresco and tempera painting) it should be 
kept under water. 

Baryta-white is absolutely unalterable by an impure at- 
mosphere, and is without action upon other pigments. It 
does not work well in oil, but a mixture of flake- white 
and baryta- white, in the proportion of 2 to i, presents the 
advantage of being very much less affected by sulphur- 
etted hydrogen than flake-white. 

The artificial baryta-white may be distinguished from 
the natural by its much finer state of division, by its 
greater body, and by the purity of its whiteness. Baryta- 
white is not adulterated, but its almost absolute insolu- 
bility in hydrochloric or nitric acid enables it to be at once 
distinguished from zinc-white or white lead. 

Several mixtures of barium sulphate and zinc sulphide 
have been introduced as pigments ; they are not suitable 
for the palette of the artist. The reaction by which the 
majority of them are formed is brought about by mixing 
together solutions of two soluble salts, barium sulphide 
(BaS) and zinc sulphate (ZnSOJ, when two new salts 
are precipitated, both insoluble, namely zinc sulphide 
(ZnS) and barium sulphate (BaSO^). 

Other white compounds used in painting are lime, 
whitening, gypsum and China-clay. These have been con- 
sidered in the chapter on Painting-Grounds. Amongst 
white pigments which we need not describe are antimo- 
nious oxide, antimonious oxychloride, lead sulphite, lead 
tungstate, lead antimonite, and lead antimoniate. Not 
only are these compounds difficult to prepare in a satis- 
factory condition of purity and whiteness, but they are 
liable to turn yellow or dull in impure air. 



156 MINOR WHITE PIGMENTS 

It should be stated here that the tests described in the 
present chapter, and in all the other chapters on pigments, 
refer only to the dry material, or, at any rate, to pigments 
mingled with no fluid other than water. If it be desired 
to operate on paints, this can be done, as a rule, only after 
the removal of the vehicle with which they have been 
ground. Oil may be removed by means of benzene or 
turpentine-spirit, gum by treatment with distilled water. 



CHAPTER XIV 

YELLOW PIGMENTS 

Yellow Ochre : Roman Ochre — Golden Ochre — Mineral 
Yellow — Bro wn Ochre — Oxford Ochre — Ocre jaiine — 
Gelber Ocker. 

The distinction between the yellow ochres and the red 
ochres, whether natural or artificial, depends upon a per- 
fectly definite chemical difference. The colour of every 
one of these pigments is due, indeed, to iron, and to iron 
in the same state of oxidation ; but the iron oxide in the 
yellow and brown ochres is chemically united to water, 
while in the red ochres it is nearly or quite anhydrous — 
that is, dry. In chemical language, then, we may say 
yellow ochre is a ferric hydrate, red ochre a ferric oxide. 
But, when we proceed to examine a number of samples 
of yellow ochre, we find, not merely different proportions 
of ferric oxide to combined water — that is, different ferric 
hydrates — but we find also very variable proportions of 
intruding or accessory constituents. In fact, yellow ochre 
represents not less than three mineral species, and it 
occurs associated with many impurities, the latter con- 
sisting mainly of silica, of clay, of rocky debris, with 
traces of gypsum, of iron or copper pyrites, and of humus 
or peaty acids. There are, moreover, ochres in which 
other compounds occur, as barium sulphate to the extent 

157 



158 YELLOW OCHRE 

of 75 per cent, in some American varieties. The three 
fundamental minerals, in order of frequency, which may 
be traced in various yellow ochres, are these : 

Brown haematite, or limomte, consisting of two mole- 
cules of ferric oxide combined with three molecules of 
water, and represented by the formula 2Fe203, 3H2O ; 

Yellow haematite, or xanthosidente, consisting of one 
molecule of ferric oxide combined with one molecule of 
water, and represented by the formula FegOg, HgO ; 

Bog-iron ore, or lymnite, consisting of one molecule of 
ferric oxide and three molecules of water, and is repre- 
sented by the formula Fefi^, sHgO; the separate exist- 
ence and permanence of a hydrate having this fornmla 
are, it must be owned, doubtful. 

It is probable that all the numerous varieties of yellow 
ochre, from the countless localities of this substance, 
belong essentially to one or other of the above species of 
iron minerals, although the frequent presence of such 
impurities or accessories as silica, iron silicates, and clay 
renders the identification very difficult. Moreover, there 
are reasons for suspecting, in some ochres at least, the 
presence of another and more complex compound, namely, 
a distinct double iron-aluminium hydrate. 

An analysis of a fine sample of yellow ochre, taken by 
the author from a pit on Shotover Hill near Oxford, gave 
the following percentages : 



Hygroscopic moisture 


- 7'i ; 


Magnesia - 


- 03 


Combined water 


- 9*0 


Silica 


■ 61-5 


Ferric oxide 


- 13-2 


Calcium sulphate 


- 14 


Alumina - . - 


- 6-3 


Undetermined - 


- 12 



The varying hues of yellow ochres depend mainly upon 
two differences of composition. One of these is the amount 
of white clay, silica, calcium sulphate, or barium sulphate 



YELLOW OCHRE 159 

present in them — this lightens the colour ; the other is the 
presence of ferric oxide, which gives them a ruddier or 
warmer hue. All, when burnt— that is, calcined — lose 
their essential water, and become converted into various 
kinds of red ochre, light red, etc. The varieties which 
contain much silica and clay (ingredients which, even in 
good yellow ochres, often amount to two-thirds of their 
weight) yield the less translucent and paler tints of some 
of the burnt red ochres. India furnishes a great variety 
of hues of yellow ochre, but our chief supplies come from 
France, Italy, Germany and Spain. More recently excel- 
lent ochres have been obtained from the district of Dubbo 
in New South Wales. Some of the English ochres (from 
Oxfordshire, Derbyshire, etc.) are of fine quality. Peri- 
gord Yellow, a natural earth found in Perigord, is a fine 
variety of yellow ochre : it yields when heated to 800°- 
1,000° C. a fine reddish orange, brighter than that of the 
light red produced from any other ochre. 

Yellow ochre is generally prepared for use as a pigment 
first of all by careful selection of the best pieces, and then 
by the familiar process of elutriation, or washing over. 
Thus it is at once freed from sand or other coarse particles, 
and from any soluble salts which it may contain. Imme- 
diately before being ground in oil, it should, however, be 
dried at a temperature a little below that of boiling water, 
as it is liable to contain hygroscopic moisture in addition 
to its necessary constitutional water. 

Yellow ochre is one of the most ancient pigments, 
having been used by the Egyptians, the Greeks, and the 
Romans. It is the oichra of Theophrastus. Pots of yellow 
ochre were found at Pompeii. It has stood, with very little 
change, the test of centuries. It certainly does become, 
in all media, but especially in oil, slightly darker and 



i6o YELLOW OCHRE 

warmer in hue after prolonged exposure to light. The 
change, however, is slight ; moreover, it soon comes to a 
stop. It is probably due in part to a slight loss of con- 
stitutional water from the ferric hydrate, and in part to 
increased translucency. It must be recollected also that 
yellow ochre as an oil-paint contains 40 or more per cent. 
of oil, and this becomes yellower and darker in time. 
Yellow ochre, so long as it is exposed to air and Hght, is 
not darkened by sulphuretted hydrogen. It is without 
action on other pigments, although the statement has often 
been made, on quite insufficient grounds, that paints which 
are damaged by contact with metallic iron are likewise 
damaged by yellow ochre and by the red oxide of iron. 
For instance, true Naples yellow is undoubtedly spoilt by 
contact with a steel spatula, because the m.etal of the latter 
takes away oxygen from, or ' reduces ' the lead antimoniate 
of which the former consists. But such an action is 
impossible with yellow ochre, for this iron compound is a 
stable substance, containing already all the oxygen it can 
take up. It is possible, notwithstanding, that ochre may 
injure the hue of some lakes, such as yellow lake and 
crimson lake, by replacing in part some of the alumina 
with which the colouring matter is united. But as such 
lakes are worthless, from their extreme instability when 
exposed to light, when used alone, such probable action 
of ochre upon them need scarcely be considered. Still 
the same action may occur in the case of the madders 
and alizarin pigments. 

Yellow ochre is little subject to adulteration, for it is 
too cheap a pigment to make it worth while to substitute 
other substances for it. But sometimes the golden and 
richer coloured varieties have been found to have had 
their colour enhanced by the addition of certain fugitive 



. YELLOW OCHRE i6i 

or semi-permanent yellows of artificial or organic origin. 
The majority of such additions may be detected by 
pouring a little liquor ammoniae mixed with spirits of 
wine upon some of the ochre placed on a filter-paper in a 
funnel : the liquid passing through will be colourless if 
the ochre be genuine. An ochre which when heated in a 
test-tube gives off, besides water, fumes which partially 
condense into a coloured or tarry matter on the glass, 
contains organic matter, naturally present or artificially 
added, and is generally of inferior permanence. Of late 
years a far more frequent adulteration of yellow ochre is 
the addition of chrome yellow — that is, lead chromate. 
This adulteration may be detected by boiling the sus- 
pected ochre with sodium carbonate solution, filtering, 
and adding to the filtrate enough acetic acid to neutralize 
it, and then a few drops of lead-acetate. A yellow pre- 
cipitate indicates the presence of a chromate. An artificial 
yellow ochre is made by acting upon solutions of iron 
salts with metallic zinc, and thoroughly washing the 
precipitate obtained. 

Brown ochre is an approximately pure limonite : raw 
sienna is very nearly related to it (see farther on), but 
cologne earth, raw umber, Caledonian brown and vandyke 
brown are distinct substances. An artificial brown ochre 
is prepared by heating yellow ochre with 4 per cent, of 
common salt to a low red heat. 

Under the name of cyprusite a peculiarly bright lemon- 
coloured earth has been imported from Cyprus as a 
pigment : it consists essentially of a hydrated ferric 
sulphate : it is not likely to prove a safe pigment for 
artistic use. 



i62 CADMIUM YELLOW 

Cadmium Yellow: Orient Yellow — Aurora Yellow — 
Daffodil — Orange Cadmium — Sulphide of Cadmium — 
Javme Brillant—Jaune de Cadmium — Kadmiumgelb, 

The metal cadmium, which is nearly related to zinc 
both chemically and physically, was discovered by 
Stromeyer in the year 1817. To one compound only of 
cadmium, the sulphide, are due all the hues and tints 
from the palest lemon cadmium to the fiery orange-red. 
This compound is represented by the formula CdS, and 
contains 112 parts by weight of cadmium to 32 parts of 
sulphur. As commonly prepared, cadmium yellow is of 
an orange hue ; when this compound separates slowly 
from a solution, or is made in any way to take a dense or 
3-ggregated form, it becomes of a decided reddish orange. 
The orange-yellow variety, when very finely ground, 
becomes less red and more incUned to yellow. Some of 
the palest cadmium yellows contain white pigments, or 
flour of sulphur, added to reduce their depth of colour : 
the presence of free sulphur is sufficient to make any 
pigment ineligible. 

There are two well-known processes for making 
cadmium yellow. In one of these pure cadmium oxide 
is heated in a covered crucible with pure sulphur in 
excess. In the other process, which yields pigments of 
greater brilliancy and beauty, a soluble salt of cadmium, 
such as the chloride or sulphate, is precipitated in the 
presence of a little free acid, by means of a solution of 
sodium sulphide, or preferably, of a stream of sulphuretted 
hydrogen. The hue of the product inclines to red when 
the solution is strong, hot and faintly acid ; to yellow 
when it is weak, cold, and neutral. It is necessary to 
state that all the materials used must be pure. Iron, 



CADMIUM YELLOW 163 

lead, bismuth, and any metals giving a coloured sulphide, 
even in traces, are seriously detrimental to the beauty of 
the product. The precipitate of cadmium sulphide, after 
having been thoroughly washed with boiling distilled 
water until the wash-waters no longer redden blue litmus 
paper, is collected on filter-papers and dried in the water- 
oven. In order to remove any free sulphur that may be 
present, the dry cadmium yellow may now be digested in 
a suitable vessel with pure carbon disulphide. After this 
treatment the pigment is once more dried, and is then 
ready for grinding in oil or other vehicle. Cadmium 
yellow, prepared by the process last described, presents 
a satisfactory degree of permanence, and has no action 
on white lead when both pigments are ground together 
in oil. But a curious change has been noticed when the 
orange-red variety of this pigment, ground in oil, was 
kept some time in the ordinary metallic collapsible tubes, 
which formerly contained some lead, although of late 
years they have been made of nearly pure tin. The 
interior surface of the tube became darkened, sometimes 
almost black, from the formation of lead sulphide. It is 
certainly strange that a similar action does not occur 
between white lead and these deep cadmiums. For I 
found that the same sample of cadmium-red in oil which 
had blackened the metallic tube, when some of it was 
laid upon flake-white in oil, and kept for years, had not 
darkened the lead compound anywhere, even at the 
surface of contact. Moreover, cadmium yellows mixed 
with flake-white prevent, as do many other substances, 
such as baryta-white, lead sulphate, etc., the ready 
darkening of this lead paint by sulphuretted hydrogen. 
On the other hand, the cadmium yellows act with great 
energy upon some of the pigments containing heavy 



i64 CADMIUM YELLOW 

metals. Emerald green, for example, is rapidly ruined 
by cadmium sulphide, both in water and in oil ; cadmium 
yellow and emerald green (Schweinfurt green) are abso- 
lutely incompatible. Chrome yellow and true Naples 
yellow are also darkened by admixture with cadmium 
yellow, at least after a time. With oil colours, a sample 
of yellow ochre, which was afterwards found to have 
been adulterated with chrome yellow to the extent of 
8 per cent, became yellowish-grey after admixture with 
some cadmium yellow. 

While the stability of what may be called the normal 
cadmium yellow or orange is pretty well assured, both as 
an oil and a water colour, a very different verdict must be 
pronounced upon pale and lemon cadmium when used in 
water-colour painting. When thus used these pigments 
do not merely fade, but acquire a somewhat greyish hue. 
The following observations throw some light upon these 
changes. During the year 1876 I prepared a number of 
samples of cadmium yellow and orange. All were obtained 
by the action of sulphuretted hydrogen upon solutions of 
cadmium chloride. The products ranged in hue from a 
lemon colour to a deep orange, according to the strength 
of the solution, the presence or absence of free acid, and 
the temperature at which the precipitation of the pigment 
took place. After due washing and drying the various 
samples were put into bottles and preserved in my labora- 
tory. They were never exposed to direct sunshine. On 
examining them from time to time it was noticed that the 
specimens of medium depth, having a yellowish orange 
hue, kept their hue perfectly, while two or three of the 
orange-red varieties exhibited a curious phenomenon of 
alteration. The loose friable lumps into which the powder 
had aggregated were distinctly paler on the outside than 



CADMIUM YELLOW 165 

in the interior, while the parts of the contents of the 
bottles which had been most exposed to light were paler 
than those which had been comparatively shaded. But a 
still more marked change had taken place in the samples 
to which the term ' pale ' cadmium might be applied. 
These had generally become still paler, almost straw- 
coloured, especially where most exposed to light ; but in 
some of the specimens orange specks were observed, 
resembling in hue what is usually called ' middle ' cad- 
mium. From the above observations it would seem that 
there is a tendency in differently tinted * wet process ' 
cadmium yellows to return to what we may call the 
normal or medium hue, but that the palest varieties are 
most subject to change. This change seems to arise in 
part from oxidation and hydration, for the bleached speci- 
mens gave indications of containing some white cadmium 
hydrate, when heated giving off a little water, and be- 
coming brownish from the formation of the brown oxide 
of cadmium. Such a bleaching of pale cadmium, if my 
explanation be correct, is in a measure explicable if we 
recollect that this variety occurs in a very fine state of 
division, and on this account is more liable to chemical 
change. In water-colour painting, where there is no 
effective protection through the presence of a hydrofuge 
medium, this fading of ' wet process ' pale cadmium is 
notorious. In oils this cadmium, like the others, is generally 
thought to be permanent. My faith in the inalterability 
of cadmium pigments, even in oil and allied media, has, 
however, been somewhat shaken during recent years. 
Cadmium orange has almost perished where used in 
Leighton's lunette * Arts of Peace,' in the Victoria and 
Albert Museum, a work executed in spirit-fresco. I 
regard the passage of the pale and of the deep cadmium 



1 66 CADMIUM YELLOW 

yellow when in powder into the normal or middle variety 
as dependent chiefly, if not entirely, upon molecular 
changes. Moreover, the pale cadmiums are rarely found 
free from admixture, and their alterability may be in part 
owing to the foreign ingredients they contain. More 
recent researches by G. Buchner and N. von Klobukoff 
confirm the conclusions drawn from my early experiments. 
There can be no doubt that cadmium sulphide exists in 
two if not in three molecular states, differing not only in 
colour but in crystalline form and in specific gravity. 
Thus pale cadmium has the specific gravity 3*9 to 4*5, 
while the red modification is denser — 4*5 to 4-8. And 
when the pale variety, dry and in powder, is rubbed 
strongly with a piece of agate, its colour deepens and 
reddens in a very decisive manner. The same change 
occurs when a water-colour wash of cadmium yellow is 
exposed for a year or so to sunlight in a perfectly dry 
atmosphere. This phenomenon is clearly analogous with 
that shown when the yellow mercuric iodide is altered 
into the scarlet form by pressure. It is perhaps safer to 
employ an ivory palette knife rather than one of steel in 
manipulating the cadmium pigments. 

Aurora yellow is a bright and beautiful pigment con- 
sisting essentially of cadmium sulphide. It has more 
opacity than most of the other varieties of cadmium and 
possesses a pure yellow hue. Its stability is greater than 
that of many other varieties of this pigment. Daffodil 
yellow is the name given to another variety of cadmium 
sulphide, prepared at a red heat and containing a small 
quantity of magnesia. Neutral orange is a mixture of 
cadmium yellow with Venetian red. 

Cadmium yellows are sometimes adulterated with 
Indian yellow, baryta and strontia chromates, and 



CADMIUM YELLOW 167 

chromates of lead. Indian yellow shows its presence by 
blackening and giving off tarry fumes when the pigment, 
in the state of dry powder, is strongly heated in a test- 
tube. The chromates may be detected by the green colour 
produced when the sample is warmed with alcohol and 
dilute sulphuric acid. The lead chromates or chrome 
yellows, and the orange and red basic chromates of the 
same metal will blacken when the substance in which 
they are present is moistened with weak ammonium 
sulphide. Free sulphur in pale cadmium yellows comes 
off as a vapour when the sample is heated, but it may be 
better detected by the solvent action upon it of carbon 
bisulphide. Baryta-white may be detected by its insolu- 
bility in hot strong hydrochloric acid, in which cadmium 
sulphide dissolves. 

Cadmium red and cadmium orange are slightly trans- 
lucent when compared with the paler and yellower varie- 
ties of this pigment, and possess very full and glowing 
hues. They work well as oil and water colours. Mixed 
with zinc-white or flake-white, deep and middle cad- 
miums yield several beautiful colours, some of which 
closely resemble the different varieties of true Naples 
yellow, and are now employed very largely in lieu of the 
latter pigment. Pure cadmium yellow, when heated 
moderately, becomes orange-red or red, but regains its 
pristine hue on cooling. If, however, the heat be con- 
siderably raised in the presence of air, some of the sulphur 
in the compound burns, and the residual mass presents 
a dull brown colour. ' Manganese oil ' accelerates the 
drying of the cadmium colours, which is sometimes 
inconveniently slow. 



168 A UREOLIN 

AuREOLiN : Cobalt Yellow — Jaime de Cobalt — Kobaltgelb. 

Origin and Composition. — This remarkable artificial 
yellow pigment was discovered by Fischer. It is a com- 
pound of the nitrites of cobalt and potassium. Usually 
it is free from water, but it sometimes contains three 
molecules, and is then represented by the formula 
KgCo2(N 02)12, 3H2O. Other proportions of water also 
occur ; but when the compound contains four molecules, 
its hue is somewhat greenish. The dry or anhydrous 
variety is best made by mixing a solution of a cobaltous 
salt, strongly acidified with acetic acid, with a concen- 
trated solution of potassium nitrite, and keeping the 
mixture warm. Perhaps a pigment of finer hue is 
obtained by passing a stream of nitric oxide gas mixed 
with air into a solution containing nitrate of cobalt and 
a little acetate of potassium ; from time to time a little 
potassium carbonate is added. 

Another method of preparing a variety of aureolin 
having a singularly bright yellow hue consists in adding 
a solution of sodium cobaltinitrite acidified with acetic 
acid to a dilute solution of potassium acetate or nitrate. 
I have tried the experiment in accordance with the in- 
structions given by Messrs. Adie and Wood (in the 
' Transactions of the Chemical Society,' vol. Ixxvii., 1900, 
p. 1076), but I have used sometimes other cobalt salts 
instead of the acetate, and have also so arranged the 
constituents of the two solutions that the precipitate of 
aureolin is intimately associated w4th barium sulphate 
precipitated at the same time. By this means an opaque 
pigment of bright and light yellow hue is obtained. The 
pure aureolin obtained by this process contains sodium 
as well as potassium, and is represented by the formula 



A UREOLIN 169 

K2NaCo(N02)6,H20. Its value as a pigment is at least 
equal to that of the better-known varieties of aureolin. 
The pure pigment prepared in the way indicated, without 
any suggestion of its use in painting, by Messrs. Adie 
and Wood, requires less oil than usual and dries well ; in 
water-colour painting it shows one distinct advantage 
over the older varieties of aureolin, for it is less soluble 
in water and does not sink into the paper. The several 
varieties of aureolin are not much affected by caustic 
potash solution or by dilute hydrochloric or nitric acid, 
and are very slowly attacked and blackened by solution 
of sulphuretted hydrogen, but are at once destroyed by 
ammonium sulphide. Ordinary aureolin is slightly soluble 
in cold water. 

Aureolin is of a pure yellow colour, and is almost trans- 
parent whether used in water or oil painting. In oil some 
samples dry with great difficulty, and become very dirty 
if exposed to the air during the progress of desiccation ; 
other samples dry and harden too quickly — the exact 
cause of this difference of deportment has not been 
ascertained. Moreover, as ordinarily ground in oil, some 
varieties require a very large proportion of the medium. 
These defects may be easily remedied by heating the 
slow-drying variety of the ground pigment to 212° F. 
immediately before the addition of the oil, and by using, 
instead of raw linseed oil, the siccative linseed oil, pre- 
pared by means of borate of manganese. Thus prepared, 
aureolin not only dries quickly, but it retains its purity 
of hue ; moreover, a surface of the dried oil pigment will 
yield nothing to a wet cloth passed over it instead of 
staining it yellow. The reason why this staining occurs 
with ordinary aureolin ground in oil, even when it has at 
last become dry, is that the oil does not suffice to pro- 



I70 AUREOLIN 

tect the particles of pigment from the solvent action of 
moisture. The quick-drying variety of aureolin should 
be ground in poppy oil. 

I find that the variety of aureolin which contains sodium 
as well as potassium (see above) dries perfectly well when 
ground in purified linseed oil, even when the latter has 
not been made siccative by special treatment. 

Aureolin properly prepared in oil, as described above, 
does not fade by exposure to sunlight, nor does it darken, 
except so far as the admixed oil is concerned. As a 
water-colour aureolin is practically permanent, even in 
sunlight, as the following figures show : 

Original intensity ... ... ... lo 

After two and five years ... ... lo 

After ten years ... ... ... 9 

In the Burlington Club trials it was found that aureolin 
stood perfectly for four years when exposed in an ordinary 
frame or in air kept dry, but that it lost somewhat by 
exposure, during the same time, in a hermetically sealed 
tube in the presence of ordinary moist air. 

The fading of fugacious organic pigments, such as the 
lakes from cochineal, is accelerated by their commixture 
with aureolin, which particularly hastens the destruction 
of indigo, even in oil. The aureolin cannot so act without 
being itself likewise affected ; it generally becomes, under 
such circumstances, of a brownish hue. 

It is easy to learn whether a sample of aureolin is free 
from combined water by heating a small portion some- 
what strongly in a long test-tube; dew will condense 
upon the upper part of the tube if water be present in the 
pigment. The presence of yellow organic matters in 
imitative or adulterated aureolins may generally be 



LEMON YELLOW 171 

detected by mixing some powder of the suspected sample 
with spirits of wine and a few drops of strong ammonia ; 
the liquid becomes red orange, or yellow if the aureolin 
be not pure. Aureolin containing chrome yellow is 
blackened by a solution of sulphuretted hydrogen. 

Aureolin is the first pigment described (in the present 
manual) which illustrates the remarkable colouring power 
of the element cobalt. The hues derived from this metal 
acting as a chromogen range from yellow to green, blue 
and violet or purple ; there is also a rose cobalt. Various 
oxides, themselves colourless, serve as chromophores. 

Lemon Yellow : Baryta Yelloiv — Barium Chromate — 
Yellow UUraniavine — Permanent Yellow — Jaime d'Outve 
mer — Zitronengelb. 

Of all the chromates which have been used in painting, 
barium chromate is the most stable. It has a pure 
yellow colour, with a not inconsiderable degree of opacity. 
It works smoothly. 

Lemon yellow is often made by mixing solutions of 
neutral potassium chromate and of barium chloride, both 
liquids having been previously heated to 100° C. A still 
better plan is to take equivalent proportions — namely, 
25I parts by weight of pure crystals of barium chloride 
and 21 J parts of pure crystals of neutral potassium 
chromate — of these two compounds, and to grind them 
together to very fine powder. Continue the grinding, and 
then add gradually sufficient pure water to convert the 
mixture into a thin paste. The paste is then heated to 
100° for fifteen minutes, thrown on a filter, washed with 
abundance of pure water, dried, and ground. 

Properly prepared lemon yellow may be mixed with 
most other stable pigments without suffering change. It is 



172 GAMBOGE 

not blackened like the lead chromes by sulphuretted 
hydrogen, but it has a tendency, as a water-colour, to 
become greenish when long exposed to this gas or to 
impure air. In oils it is very useful, for although some 
organic pigments may give it a greenish cast by reducing 
it in part to green chromic oxide, yet it may be safely 
associated with aureolin, with madder carmine, and with 
Prussian blue. Lemon yellow may be used in fresco. 

Strontium chromate is very often — we may say gener- 
ally — substituted for true lemon yellow, but it is less 
stable, and has the further defect (for water-colour work) 
of being decidedly soluble even in cold water, so that 
light washes of it may be found to sink into the paper 
and to partially disappear. The most common adultera- 
tion of lemon yellow is with pale chrome ; of course, 
sulphuretted hydrogen detects this falsification by darken- 
ing or blackening the pigment. Strontium chromate is 
distinguished from barium chromate by its dissolving in 
boiling water to such an extent as to yield a solution 
having a strong yellow colour. It may be prepared in 
the same way as the chromate of barium. Zinc chromate 
and calcium chromate are yellow pigments of inferior 
value. A mixture of zinc chromate with barium chromate 
is sold as primrose yellow. 

Gamboge : Gomme-gutte — Gummigutt. 

Origin. — This gum-resin is produced by several species 
of Garcinia. Siam gamboge comes from G. Hanhuryi 
(Hook, f.) ; Ceylon gamboge from G. Morella (Desv.). 
There are other species from which the same product is 
obtained in various parts of India, as G. Camhogia 
(Desrouss.) and G. elliptica. The fine, deep-coloured 



GAMBOGE 173 

gamboge, produced by the Burmese G . heterandra (Wall.), 
may prove to be superior to Siam gamboge, but it has 
not yet become an article of European trade. Gamboge 
is a mixture of a gum soluble in water, and a resin which 
is soluble in alcohol, chloroform, ether, etc. The pipe- 
gamboge of Siam, which is as pure as any variety met 
with in commerce, contains about 78 per cent, of resin 
and 18 of gum. The resin, which is the true colouring- 
matter, may be easily obtained pure by crushing pipe- 
gamboge into fine powder, mixing it with a little water, 
and then shaking up the mixture with ether ; the ether 
dissolves the resin alone. From the ethereal solution the 
colouring-resin is recoverable by evaporation ; but it is 
better to add a little drying-oil and some copal- varnish 
before driving off the ether by means of a very gentle 
heat. The coloured, semi-fluid mass which then remains 
may be preserved in bottles or tubes for use as an oil- 
paint. The resin of gamboge has the properties of an 
acid, and forms yellow, orange, or brown compounds, 
with soda, lime, baryta, and other bases. Some of these 
compounds might prove useful as paints. 

Gamboge was used by the early Flemish oil-painters. 
In the seventeenth century it was largely employed to 
give a golden hue to the embossed leathers for which 
Amsterdam was famous. 

In water-colour painting gamboge is not trustworthy. 
It is unaffected by sulphur compounds, but is darkened 
by ammoniacal fumes, and slowly bleached by strong 
light. Some samples prove, however, far less fugitive 
than others. In two years' exposure to sunlight, one 
sample of cake-gamboge lost more than half its original 
intensity ; while a sample of moist gamboge, bought at 
the same time from the same maker, retained nine-tenths. 



174 INDIAN YELLOW 

The same sample of moist gamboge, after seven years, 
still showed seven degrees out of the original ten of 
intensity. 

As an oil-colour, gamboge affords a rich, transparent, 
golden or amber hue ; it has some claims to the con- 
sideration of artists. To secure its permanence, ad- 
mixture with oil alone does not, however, suffice ; a resin 
such as copal, or Strasburg turpentine, or wax, or 
paraffin, must be used also. Some of Sir Joshua 
Reynolds' trials of gamboge prove this, those with oil 
alone being a name only now ; while those with resin, or 
wax, retain their original hue very fairly, though they 
were spread upon the canvas in 1772. It must, there- 
fore, be remembered that reliance cannot be placed upon 
the permanence of the ordinary gamboge oil-paint as 
met with in commerce. 

Gamboge, from its resinous nature, shows, when laid 
on thickly as a water-colour, a rather shining surface. 
It appears to have little or no chemical action on other 
pigments (with the exception, perhaps, of white lead), 
although, if it be mixed with anything which contains 
lime, or other alkaline compounds, it becomes brownish, 
and darkens. Gamboge forms beautifully clear and rich 
greens with Prussian blue or indigo, but its place in 
water-colour painting may be advantageously taken by 
aureolin, and even by Indian yellow. When mixed with 
baryta yellow or cadmium yellow, the permanency of 
gamboge is enhanced. 

Indian Yellow : Piuri, Ptirree, Peori — Jatme Indien — 
Indischgelb. 

This remarkable pigment is obtained at Monghyr, a 
town in Bengal, from the urine of cows which have been 



INDIAN YELLOW i75 

fed upon mango-leaves. It generally occurs in the 
bazaars of the Panjab in the form of large balls, having 
an offensive urinous odour. 

Indian yellow is an impure magnesium salt of euxanthic 
acid. The essential part of it is a compound containing 
4*5 per cent, magnesia, 187 per cent, water, and 787 
per cent, euxanthic anhydride; but this substance is 
always associated, even in the most carefully purified 
samples of prepared Indian yellow, with various im- 
purities both mineral and organic. The pure mag- 
nesium euxanthate is represented by the formula 
CisHieMgOii, 5H2O. 

For artistic purposes the crude imported Indian yellow 
is thoroughly powdered, and then washed with boiling 
water, until the liquid filtered from it is no longer 
coloured ; a brown impurity, and much of the evil smell, 
are thus removed. The colour of the washed product is 
enriched by leaving it in contact for a day or two with a 
saturated solution of sal-ammoniac, and then repeating 
the treatment with hot water. 

Thus purified, this pigment presents a translucent 
orange-yellow colour of great depth and beauty. Ground 
in oil, some specimens are practically unchanged, even 
after long exposure to sunlight, any darkening they show 
being due either to imperfect purification, or to the 
change of the associated oil. Such change is reduced to 
a minimum if poppy oil be substituted for linseed oil, or 
if the latter be previously treated with manganese borate. 
On the other hand, I have met with specimens of Indian 
yellow ground in oil which, after five years' exposure, 
have lost nearly one-third of their original depth, and 
have, at the same time, become rather reddish-brown in 
hue. As a water-colour, Indian yellow retains its hue 



176 INDIAN YELLOW 

unimpaired when exposed to diffused daylight ; sunlight 
very slowly bleaches it, the hue it acquires being some- 
what brownish. The rate of alteration and of reduction 
in force caused by sunlight may be approximately repre- 
sented by these figures : 

Original intensity lo 



After 2 years 
After 5 years 
After 7 years 
After 10 years 



When this water-colour pigment is exposed to sunlight 
in the presence of air maintained in a state of perfect 
dryness it loses its colour much more rapidly than under 
ordinary conditions. For this reason it may be advisable 
to incorporate an extra proportion of glycerin with Indian 
yellow when prepared as a water-colour. 

As a general rule, Indian yellow suffers no change by 
admixture with any pigment itself permanent, nor is it 
affected by sulphur compounds. True Naples yellow, 
however, most of the chromates, and probably aureolin 
alsO;, tend to embrown it to some extent. 

Indian yellow which has been adulterated with lead 
chromate (chrome yellow) becomes dark-brown when 
moistened with ammonium sulphide. 

A fine yellow pigment may be prepared from the 
euxanthic acid, which is the characteristic constituent of 
Indian yellow, by throwing it down in combination with 
the two bases — alumina and magnesia. The following 
directions may be followed : Dissolve i part of pure 
euxanthic acid in just sufficient dilute ammonia. Pour 
the solution into a liquid prepared by dissolving 45 parts 
of potash-alum, 15 parts Epsom salts, and 6 parts sal- 



MARS YELLOW 177 

ammoniac in 250 parts of water. Now cautiously add 
dilute ammonia to the mixture, stirring all the time, and 
avoiding any excess of ammonia. The precipitated pig- 
ment is to be thoroughly washed, and then pressed, dried, 
and ground. 

Mars Yellow: Mars Orange — Artificial Ochre — Jaime 
de Mars. 

This pigment is a kind of yellow ochre prepared arti- 
ficially. It may be made by precipitating a salt of iron 
mixed with alum by means of caustic soda, or potash, 
or lime. The salts of iron used are either green vitriol 
(ferrous sulphate) or the ferric chloride. If green vitriol 
be employed the precipitate formed gradually becomes 
yellow on exposure to the air. Upon the proportion of 
alum mixed with the iron salt depends the depth of the 
yellow colour in the product, for the alumina precipitated 
with the iron hydrate acts as a diluent of the colour. 
When lime is used as a precipitant for the iron com- 
pound (if this be green vitriol or ferric sulphate), calcium 
sulphate, that is, gypsum, comes down along with the 
ferric hydrate and basic ferric sulphate, and serves to 
lighten the colour. 

By submitting the different varieties of Mars yellow 
to various degrees of heat, with or without a little nitre, 
a number of products of different hues are obtained, in- 
cluding Mars orange. Mars red, Mars brown, and Mars 
violet. All these preparations require very thorough 
washing to fit them for use on the palette of the artist. 

The Mars colours are permanent when carefully pre- 
pared and thoroughly purified from soluble salts. They 
seem sometimes to have a slightly injurious effect upon 
a few of the best semi-permanent pigments of organic 

12 



178 NAPLES YELLOW 

origin, such as the madder colours. This action may be 
due to the ferric hydrate in them combining with the 
colouring matter, and displacing some of the alumina 
previously united with it. In this direction it is probable 
that Mars yellow will be more active than the deeper- 
coloured pigments produced by calcining it at various 
temperatures. 



Naples Yellow : Jaune de Naples — Jaune d'Antimoine 
— Neapelgelh — Giallo di Napoli. 

Under this name three different substances are in- 
cluded. The pigment generally sold in England as 
' Naples yellow ' is an excellent imitation made by mixing 
cadmium yellow or deep cadmium with a white, prefer- 
ably a zinc white. But a true Naples yellow, which is 
a basic lead antimoniate, is still procurable from some 
artists' colourmen. This preparation is sometimes made 
by heating together for two hours a mixture of i part 
tartar emetic, 2 parts nitrate of lead, and 5 parts common 
salt, all the ingredients being of the purest quality, and 
the heat not exceeding that at which common salt fuses. 
A more recent process, in which zinc oxide is introduced 
among the materials which are heated together, yields a 
paler but excellent product. K bright pale variety of 
yellow ochre seems to have formerly gone under the 
name of Naples yellow. 

This antimonial yellow has been known from very early 
times as an enamel colour. It has been found upon 
Babylonian bricks at least 2,500 years old. Persian 
pottery as early as the thirteenth century of our era is 
occasionally decorated with antimonial yellow. 

In oil the genuine and the imitative Naples yellows 



NAPLES YELLOW 179 

are quite permanent, so far as light is concerned, but the 
genuine kind is liable to be darkened, like other lead 
compounds, by air containing sulphuretted hydrogen. In 
water-colour painting genuine Naples yellow is quite in- 
admissible, for it blackens rapidly, but irregularly, in the 
presence of mere traces of sulphur compounds. This 
blackening, like that of lead white under similar con- 
ditions, is much more marked in darkness than in light. 

Naples yellow, in contact with metallic iron, tin, 
pewter, zinc, and several other metals, is discoloured and 
blackened. An ivory instead of a steel spatula, or palette 
knife, should be used with this pigment. The darkening 
in question is due in part to attrition, owing to the 
extreme hardness of the particles of the lead antimoniate, 
however finely the material may have been ground, and 
partly to the reducing effect of the above-named metals 
upon this antimoniate. Iron in the form of its oxide or 
hydrate (as in light red or yellow ochre), or in complex 
combinations (such as Prussian blue), does not exert any 
effect upon Naples yellow. A statement to the contrary 
effect has crept into a large number of technical manuals, 
but I have been unable to discover the slightest experi- 
mental evidence in favour of such a view. Naples 
yellow, however, is injured by and does injure some of 
the organic pigments, such as the cochineal reds and the 
numerous yellow lakes. But as Naples yellow cannot 
be used as a water colour, and as the above-named 
organic pigments ought to be entirely excluded from the 
palettes of all artists, the action in question is of little 
importance. Naples yellow acts upon indigo also. 
Indigo, however, is a pigment, to which a very high 
degree of permanence cannot be assigned ; there is, 
moreover, no reason why it should be associated with 



i8o YELLOW LAKE 

Naples yellow, as other yellow pigments may be safely 
used to modify its hue. 

Another pigment also is sold as jaune d'antimoine. It 
is a mixture of the oxychlorides of bismuth and lead with 
lead antimoniate. When carefully prepared it yields a 
rich paint of good body, but its use cannot be recom- 
mended to artists. 

Yellow Lake : Brown Pink — Citrine Lake — Yellow 
Madder — Italian Pink — Quercitron Lake — Gelhev Lack. 

Origin. — The sources of yellow lake are numerous, but 
the best kind is obtained from quercitron bark from 
Quercus tinctoria, Qu. nigra, and Qu. citrina, three species 
of North American oak. A hot-water decoction is made, 
and this is precipitated by a solution of alum and dilute 
ammonia. A richer yellow pigment is obtained by 
extracting the powdered bark and alburnum with boiling 
dilute sulphuric acid instead of with water. The original 
colouring matter of the bark (quercitrin) is thus changed 
into a more stable compound known as quercetin. The 
former substance is a glucoside, the latter has the 
character of an acid ; both may be converted into lakes 
by bringing them into contact with precipitating or pre- 
cipitated hydrate of alumina. Yellow lake was formerly 
made from the fruits of various species of buckthorn, 
known as Persian, Turkish, or Avignon berries. The 
species yielding these fruits are Rhamniis infectorius, 
R. oleoides, R. saxatilis, R. amyi^dalinus, R. catharticus. The 
bark of R. frangnla and of R. catharticus also yields a 
yellov/ pigment. * Stil de grain,' and several of the con- 
tinental yellow lakes, are made from the above-named 
berry. 



BROWN PINK 



i8i 



Italian pink, Dutch pink, and deep yellow madder are 
names usually given to the richer yellow lakes of quer- 
citron, although some of these pigments are occasionally 
prepared from Turkish or Avignon berries. 

Beautiful and useful as many yellow lakes undoubtedly 
are, they should be rigorously excluded from the artist's 
palette. In oil most of them are very bad driers, as well 
as fugitive : in water-colour they generally lose nine- 
tenths of their colour within two years of exposure to 
sunlight : the residual stain is ultimately of a bluish-grey. 

The following observations as to the behaviour of 
several members of this group, on exposure for two years 
to sunlight, apply to the colours as ground in oil, and as 
mixed with flake- white in tint : 



Name 


/« Oil only 


With 

Flake- white 


Original 
Intensity = 10 


Laque Robert — hell- 










gelb - - - 


Lemon yellow •■ 


Pale straw - 


- 2 


^ 


Laque Robert— dun- 








1 


kelgelb - 


Deep lemon 


Stone - 


- 4 


8 


Laque brun-jaune 


Salmon - 


Pale rose - 


- 7 


*« 


Laque brun-fonce 


Yellowish -grey 


Smoke-grey 


- 8 


1 


Pale yellow madder - 


Pale orange 


Pale buff - 


- 7 


K 

^ 


Deep yellow madder - 


Greyish salmon 


Pale greyish 


pink 6; 



The same pigments used as glazing colours over flake- 
white have faded to about the same extent, but their 
change of hue is, in one or two cases, rather less marked. 

The so-called brown pink is usually a deep quercitron 
lake, although it was formerly made from the berries of 
one of the kinds of buckthorn (Rhamnus) previously 
named. I have never met with a specimen of it which 
would stand a year's exposure to sunlight without suffer- 
ing almost complete change or loss of colour both in Vv^ater 
and in oil. And it further presents the awkward effect of 



1 82 CHROME YELLOW 

becoming ultimately of a cool bluish-grey hue, a change 
particularly unfortunate when it has been freely used to 
represent foreground vegetation, or the golden lights on 
the near foliage of trees. Yet I am bound to confess 
that in Mr. W. Simpson's fifteen years' trial of certain 
water-colour pigments, the brown-pink has suffered com- 
paratively little alteration. Had a portion of the original 
cake-colour employed been preserved for examination it 
might have been possible to have discovered the cause 
of this anomalous behaviour of the particular specimen 
in question. 

Chrome Yellow : Chrome — Chromate of Lead — Jaune de 
Chrome — Chromgelb. 

This pigment, when of a pure yellow hue, is the neutral 
lead chromate. By associating it with an additional 
quantity of lead oxide it may be obtained of various 
orange and reddish orange hues. It may be made by the 
mutual action of a soluble lead salt, such as the acetate 
or nitrate, and the chromate or bichromate of potassium. 
Or white lead in fine powder (2 kilos.) may be boiled with 
a solution of bichromate of potassium (J kilo.) in water 
(10 litres). Alum and baryta-white, or lead sulphate, are 
also employed in the preparation of some of the paler 
chrome yellows. Lemon chrome is a mixture of lead 
chromate and sulphate. Orange chrome and chrome red 
are prepared from a mixture of lead acetate (6f kilos.), 
litharge (5J kilos.), neutral potassium chromate (6 kilos.), 
caustic potash being sometimes used in addition. Chrome 
red may be obtained also by the direct action of caustic 
soda in solution upon the yellow lead chromate : its 
chemical formula is PbCrO^, PbO, or Pb2Cr05. 



VANADIUM YELLOW 183 

The chromates of lead are peculiarly liable to change, 
and are quite unfitted for use in tempera or water-colour 
painting. In oil, especially if protected by varnish, or 
locked up in a resinous vehicle, these pigments show a 
certain measure of permanence, except when they are 
mingled with paints of organic origin. In fact there are 
two causes which militate against the integrity of the lead 
chromates. One of these is the tendency which they 
possess towards reduction, that is, the loss of oxygen by 
their chromic constituent, by which the green or lower 
oxide of chromium is formed. This change is brought 
about by many kinds of organic matter, notably by such 
animal or vegetable pigments as are themselves prone to 
oxidation. The other cause of deterioration is the pres- 
ence of certain sulphur compounds which act upon the 
lead chromates in the same way as they act upon white 
lead, producing lead sulphide of a dark brown, or a grey 
colour. 

Of late years the respective merits as oil-paints of 
cadmium yellow and chrome yellow have been warmly 
contested ; the tendency at present, especially among 
artists rather than among chemists, is to give a verdict 
in favour of the latter pigment. 

Vanadium Yellow. 

It has been proposed to employ the beautiful golden- 
bronze crystals of meta-vanadic acid as a pigment. They 
possess, when finely ground, an intense colour, like that 
of a very rich golden ochre, but less earthy, and more 
brilliant. This pigment has remarkable covering power, 
and works admirably both as an oil and a water-colour. 
Although the material is somewhat costly, the price for 
which it could be prepared need not preclude its use. 



1 84 KINGS' YELLOW 

But, unfortunately, this colour is not permanent. A few 
hours' exposure to sunshine of a water-colour wash of 
vanadium yellow suffices to change and deteriorate its 
hue in a marked degree. 

Kings' Yellow : Orpinient — Jaime Royal — Konigsgelb, 

The yellow arsenious sulphide (AsgSg), though extremely 
beautiful in hue, cannot be relied on as a pigment. Even 
in oil or varnish its colour fades : Sir Joshua Reynolds' 
experimental canvas shows some pale brown patches 
which have once been kings' yellow, but which now have 
almost entirely disappeared. Strange to say, in one of 
his trials, a few quite visible crystals of orpiment are 
preserved. As it cannot be imagined that he used this 
pigment in this exceedingly coarse form, it would seem 
that a molecular aggregation of a part of the orpiment 
has taken place in the lapse of years. If this change has 
not occurred, then we may conclude that only the largest 
particles of the kings' yellow have escaped alteration. 
Under any circumstances the inadmissibility of kings' 
yellow to the palette of the artist is obvious : moreover, 
it cannot be safely mixed with any pigment containing 
lead or copper. It was known to the Egyptians. 

Another compound of arsenic and sulphur (rVsgSg) has 
been employed as a pigment. It is of an orange-red hue 
and is known as realgar. Not only is it extremely poison- 
ous, but it sufi'ers change on exposure to light, and acts 
injuriously upon colours containing copper or lead. It was 
used by the Romans : I identified a fragment of it amongst 
the objects discovered at Silchester in the year 1896. 



PURE ORANGE 185 

Pure Orange : Marigold — Alizarin Yellow — Alizarin 
Orange. 

Under the above names a pigment of great richness 
and beauty has been introduced. It is a kind of lake, 
and consists of a coal-tar colour known to chemists as 
/3-nitro-alizarin thrown down upon an aluminous base. 
Nitro-alizarin, as its name implies, is a derivative of 
alizarin, one of the least changeable of all organic pig- 
ments, and the chief tinctorial product of madder. There 
is no doubt about the beautiful hue of this paint, a deep 
brownish gold : the trials first made as to its permanence 
in oil promised well, but on continuing the exposure to 
light of this pigment ground in oil it became evident that 
it suffered considerably. The deterioration was more 
marked when the paint had been mixed with flake white, 
but even as a glazing colour it is not safe. 



CHAPTER XV 

RED PIGMENTS 

Vermilion : Cinnabar — Vermilion — Zinnohev. 

The mineral cinnabar, or mercuric sulphide, occurs in 
many parts of Europe, and abundantly in China, and is 
extensively worked in New Almaden in California ; it 
would be tedious to recount the numerous localities in 
which it has been, or is, found. Its colour in the mass 
varies from cochineal-red and red-brown to lead-grey ; its 
powder is usually scarlet, or red. Its hardness lies 
between that of gypsum and that of calc-spar. It seldom 
contains even i part in loo of impurities, but consists in 
loo parts of very nearly 14 parts of sulphur by weight, 
united with 86 of mercury, or i atom of each element. 
The density of native vermilion is about 9. Vermilion 
was formerly known as vermiculus, cinnabaris, ceno- 
brium, and minium ; the last name is now appropriated 
to red lead. Vermilion and vermiculus are derived from 
the Latin vermes^ a name originally designating the 
'kermes' insect found on the ilex or evergreen oak, which 
is still used for the preparation of a red dye. From 
kermes, in its turn, the words crimson and carmine are 
derived. The name cinnabar is supposed to be of 
Oriental origin (compare the Persian zanjifrak), and was 
used sometimes to designate dragon's blood, a red resin. 

186 



VERMILION 187 

Theophrastus informs us that two kinds of cinnabar were 
known to the Greeks. One of these was undoubtedly 
real cinnabar (chiefly from Spain), the other was red 
lead. PHny's * cinnabar ' or ' minium ' was true ver- 
milion, so was the * minium ' of Vitruvius. Theophilus 
calls it 'cenobrium,' Wyclif 'cynoper,' Hakluyt * cinaper,' 
and Ben Jonson * cinoper.' 

One of the most curious facts concerning vermilion is 
that it is identical in the nature and proportion of its 
two constituent elements with an artificial black sub- 
stance, ' ^thiop's mineral/ The red substance may be 
changed into the black, and vice versa, and this without 
any loss or gain, or any alteration of chemical com- 
position, the change being a physical or molecular one 
merely. The black substance is amorphous, the red 
crystalline. 

The pigment vermilion may be made by simply grind- 
ing selected pieces of native cinnabar, or it may be 
obtained artificially by combining the two elements 
sulphur and mercury. 

All the methods of preparing vermilion artificially may 
be grouped under two divisions. The first of these is the 
dry way, the other the wet way. In the former method 
metallic mercury 42 parts, and sulphur 8 parts, are inti- 
mately mixed and agitated together in revolving drums 
until they have combined. The brownish-black powder 
thus obtained is then submitted to sublimation in vertical 
iron cylinders, surmounted by heads which are connected 
with receivers. On sufficient heating, the mercuric sul- 
phide sublimes as cinnabar or vermilion, the best part 
condensing in the retort-heads. The rest of the sublimed 
product (which has travelled farther) contains free sul- 
phur, and is of inferior colour. The selected portions are 



1 88 VERMILION 

next ground, moistened with water, warmed with a Httle 
caustic potash solution or nitric acid, and then thoroughly- 
washed with boiling water. In another dry process the 
mercury is gradually added to the proper proportion of 
melted sulphur in an iron basin. When the combination 
(which is accompanied by a violent evolution of light and 
heat) is complete, the fused blackish mass is poured out, 
broken into fragments, heated until excess of sulphur has 
been driven off, and then sublimed in the way already 
described. Some makers add to the crude sulphide, pre- 
vious to sublimation, i per cent, of antimony sulphide, 
with the object of improving the colour ; the product is 
afterwards ground, digested with liver of sulphur, and 
then washed with hydrochloric acid. 

There are numberless processes for preparing vermilion 
by the wet way. One of the best of these consists in 
grinding, in the presence of water, lOo parts of mercury 
with 38 parts of flowers of sulphur until these elements 
have united. The black product is then triturated at 
45° C. for many hours with a solution of 25 parts of 
caustic potash in 150 parts of water. When the product 
has attained its maximum of redness and beauty, it is 
thrown into water, and thoroughly washed by decantation. 
In a second process mercury, sulphur, and potassium 
pentasulphide are boiled together for three or four hours, 
and then the mixture is kept at a temperature of 50° C. 
for several days. Vermilion may also be prepared from 
the black sulphide obtained by precipitating a mercuric 
salt with a soluble sulphide, from ' white precipitate,' and 
from metallic mercury itself, by warming any one of these 
substances with a solution of an alkaline pentasulphide, 
and then purifying the product by means of a potash- 
solution heated to 45° C. It has also been found that ver- 



VERMILION 189 

milion is produced when a mixture of mercurous chloride 
(calomel) and zinc sulphate is heated to 45° — 50° C. with 
an excess of a solution of sodium thiosulphate. 

Except where carmine or realgar (red sulphide of 
arsenic) is present, a very simple test suffices to ascertain 
whether vermilion be pure or not. A small pinch should 
be heated over a spirit-lamp on a fragment of hard porce- 
lain ; no appreciable residue will be found, unless red- 
lead, red iron oxide, brickdust, or other non-volatile 
adulterants be present. Carmine, which is sometimes 
added to scarlet vermilions to approximate their hue to 
that of the crimson varieties such as the Chinese, may be 
detected by laying a pinch of the powdered pigment on a 
small pad of white blotting-paper, and moistening the 
substance with a few drops of strong ammonia-water ; a 
crimson stain will appear on the paper if carmine or 
crimson-lake be present. The colour of a good vermiHon 
is not changed by moistening it with nitric acid. The 
accidental impurities which impair the hue of vermilion 
are free sulphur, and compounds of iron and lead ; that 
prepared in the wet way often retains alkaline salts, 
owing to imperfect washing. A spurious vermilion, 
called anti-vermilion or antimony vermilion, is made by 
warming antimonious chloride with sodium thiosulphate 
solution. It is the chief material used in colouring red 
rubber. 

Vermilion prepared from the mineral or native cinnabar 
is probably less liable to change than the artificial pro- 
ducts, whether obtained by the dry way or the moist way ; 
but • moist way ' vermilions are certainly the most alter- 
able. And it may also be remarked that the more finely 
a vermilion is ground, the less stable it is — at least, as a 
water-colour paint. Thus it happens that, other things 



igo VERMILION 

being equal, an orange-vermilion is inferior in perma- 
nence to a scarlet, and a scarlet-vermilion to one inclining 
to crimson. As an oil-pigment, vermilion does not dry 
well, but suffers, especially if it be locked up in copal or 
paraffin, no change by light or impure air ; loo parts of 
the dry substance require less than 20 parts of oil. Owing 
to its great density, vermilion tends to separate from the 
oil with which it has been ground. This result may be 
obviated by the addition to the oil of a little aluminium 
oleate or linoleate, or by the employment of oxidized and 
thickened oil in which a small quantity of beeswax or 
ceresin has been dissolved by the aid of heat. In water- 
colour painting most vermilions are found to be changed 
on exposure, the solar rays gradually converting the red 
into the black modification of mercuric sulphide, without, 
of course, producing any chemical alteration. This 
change occurs even in the absence of air and of moisture. 
Impure air, per se, even if sulphuretted hydrogen be 
present, does not discolour vermilion. 

Anyone who has examined old illuminated manuscripts 
must have noticed the apparent capriciousness with which 
the ornaments, and especially the initial letters, painted 
with vermilion, have been afifected. I have more than 
once observed that, while all the vermilion used in one 
part of a missal or choral-book has remained red, a leaden 
hue has spread irregularly over the rest of the work in 
places where this pigment has been used. This may be 
due to the use by the illuminator of a sample of vermilion 
adulterated with minium or red lead, but sometimes to a 
change in the technique, as a change in the style or handi- 
work is often associated with the difference above de- 
scribed. In oil-painting there are no permanent pigments, 
save the copper-greens, with which vermilion may not be 



VERMILION 191 

safely mixed. Only when it contains impurities, such as 
free sulphur, does it darken flake-white. 

Vermilion prepared from native cinnabar is found per- 
fectly preserved in the flesh-tints of Italian tempera- 
paintings of the thirteenth and fourteenth and fifteenth 
centuries. It has stood in the wall-paintings of Pompeii, 
where it often seems to have been waxed. A compara- 
tively recent but instructive instance of the permanence 
of vermilion in oil is furnished by a portrait, dated 1758, 
in the National Portrait Gallery. It represents the painter, 
Hogarth, with his palette set before him. The second of 
the dabs of colour thereon is vermilion, perfectly intact. 
In the same collection there is a portrait by Marc Ghee- 
raedts of Mary Sidney, Countess of Pembroke, in which 
the vermilion has stood. This work was painted in 16 14. 
Scores of earlier and later examples might be cited. 

The variations in hue observable in different specimens 
of vermilion are mainly due to the differing degrees of 
fineness in which the pigment occurs. The coarsest grain 
corresponds with a crimson hue, and then we have every 
variety of colour ranging from scarlet to reddish orange 
or orange. The processes of regrinding and 'washing- 
over ' enable us to obtain the kinds separately. And if we 
repeat these operations often enough, we may ultimately 
convert the whole of a crimson vermilion into the orange 
form. It was formerly supposed that the latter material 
was a mere scum, or impurity, or at least differed from the 
crimson kind in composition. When any vermilion is 
mixed in tint with white, an opposite effect to that of 
further grinding is produced. For, as the early writer 
Eraclius states : ' If you mix white with vermiculus, car- 
mine is made ' — that is, the hue of the mixture becomes 
more rosy, and therefore further removed from orange. 



192 MADDER PIGMENTS 

Madder : Pink Madder — Rose Madder — Madder Carmine 
— Madder Red — Rubens' Madder — Madder Purple — 
Madder Lake — Madder Brown — Carmin de Garance — 
Laqtie de Garance — Krapplack. 

Some authorities assert that madder was used in dyeing 
long before its employment in painting. But there is some 
evidence, derived from ' finds ' of pigments and from paint- 
ings, that the ancient Greeks and Romans were acquainted 
with a pink pigment derived from madder, while there 
are good reasons for believing that such substances were 
widely known in Europe as early as the thirteenth century. 
Even in England, such a pigment is almost certainly re- 
ferred to, under the name ' sinopis,' in the middle of the 
fourteenth century. Now Alcherius (close of fourteenth 
century) tells us that ' sinopis is a colour redder than ver- 
milion, and it is made from varancia.' * Varancia ' is 
clearly garance — that is, madder — the same material being 
named ' warancia ' and ' waranz ' in a British Museum 
manuscript (Sloane, No. 416) which contains recipes of 
the fourteenth century. Besides ' sinopis ' (strictly, a red 
earth), madder-lake was called, in English account-rolls of 
the fourteenth century, * sinopre ' and * cynople.' It is, 
however, difficult, if not impossible, to ascertain the pre- 
cise date at which pigments derived from madder came 
into use in the various schools of painting in Europe. For 
the nomenclature of pigments has always been somewhat 
vague, while the evidence furnished by existing pictures 
does not at present enable us to trace back with absolute 
certainty the mediaeval use of madder paints to an earlier 
time than the fifteenth century. Eraclius does not men- 
tion madder, nor does Cennini, who lived at a much later 
time. Mr. R. Hendrie, in his notes to ' Theophilus,' 



MADDER 193 

speaks of an English manuscript of the fourteenth century 
in which directions are given for extracting the colouring 
matter of ' madyr.' From these directions we are, per- 
haps, justified in concluding that the preparation of a kind 
of liquid paint was intended. 

The European madder-plant, a native of Greece, belongs 
to the tribe Galiese, of the order Rubiaceae ; it is the Ruhia 
tinctomm of Linnaeus, Several other species of this genus 
are used or grown in India for the sake of the red dye they 
afford. Among such species, Riihia covdifolia (Linn.) and 
R. sikkimensis (Kurz.) may be named, but the European 
madder is also cultivated extensively in India. Much 
madder was formerly grown in the Levant, in Holland, 
and in the south of France ; but the manufacture by arti- 
ficial means from the anthracene of coal-tar of its two chief 
colouring matters, alizarin and purpurin, has almost en- 
tirely extinguished the cultivation of the madder-plant in 
Europe. We shall have something to say presently con- 
cerning the artificial products above named. 

The root of madder contains a much larger proportion 
of the colouring matters (or, it would be more correct to 
say, colour-making substances) than the other parts of 
the plant. They occur dissolved in the yellow cell-con- 
tents of the soft tissue of the root. The finest madder 
was grown in the ' Palud,' a chalky valley near Vaucluse. 
But the cultivation of this plant was carried out in great 
perfection in Zeeland during the eighteenth century. 

The colouring matters obtained from madder exist in 
the plant in the form of glucosides. These glucosides are 
resolved by the fermentation, brought about by a peculiar 
ferment in the plant itself, and by many chemical agents, 
such as mineral alkalies and acids, mainly into glucose on 
the one hand, and on the other into the several colouring 

13 



194 MADDER LAKES 

principles. Of such colouring principles the glucosides in 
madder yield at least three, of which the most important 
are these two : 

1. Alizarin, C^^HgO^. 

2. Purpurin, Cj^^HgOg. 

Both alizarin and purpurin are now manufactured arti- 
ficially from anthracene. This compound, which occurs in 
coal-tar, is a crystalline fluorescent hydrocarbon, C^^H^q. 
By a series of processes this substance gives rise to alizarin 
and purpurin, which are in all respects identical with these 
colouring matters as derived from, the madder plant itself. 
The artificial alizarin of commerce contains several other 
colouring matters, two of which are better known than the 
others ; these are anthrapurpurin (C^^HgOg) and purpuro- 
xanthin (Cj^^HgO^). Purpuroxanthin is also present in the 
natural pigments derived from madder, but it exists in 
small proportion. Of all these compounds alizarin is the 
most important and the best known, and yields lakes 
having various hues of crimson, rose, purple, violet and 
marone, according to its purity, its concentration, and the 
nature of the base (alumina, aluminium phosphate, iron 
oxide, manganese oxide, copper oxide, or lime with 
alumina) with which it is associated. The purpurin and 
anthrapurpurin resemble one another closely, and give 
pigments which are generally characterized by more 
orange or red hues than those obtained with alizarin. 
The rose and pink madders and the madder carmines of 
commerce are generally so manufactured as to include, 
for their colouring constituents, much alizarin and very 
little purpurin. A few indications of the ordinary methods 
of preparing these lakes may first be given. 

The material used is often that called * madder flowers,' 
which consists of the finely ground dried root after it has 



MADDER LAKES 195 

been submitted to the action of dilute sulphuric acid and 
washed. Four pounds of this madder are taken and 
warmed for two or three hours on a steamer, with a solu- 
tion of I pound of pure alum in i gallon of water. The 
mixture is placed in a filter-press, and the liquor obtained 
(which must be perfectly clear) precipitated by the gradual 
addition of a solution of sodium carbonate. The first 
portions of madder lake which fall, being the best, should 
be collected apart. All the precipitates should be 
thoroughly washed with rain or distilled water till the 
wash-waters are no longer troubled on the addition of 
barium chloride solution; they are then moulded into small 
cones, drops, or discs, and carefully dried at a moderate 
temperature. Another process for preparing madder lakes 
is a modification of the above. Four pounds of madder- 
root in powder, after having been fermented and then 
washed with a weak solution of sodium sulphate, are 
boiled for fifteen minutes with 4 gallons of a 10 per cent, 
solution of pure alum, the whole is filtered, and at a tem- 
perature of 45° partially neutralized with a solution in 
water of about 8 ounces of pure sodium carbonate. The 
liquor is now brought nearly to the boiling-point ; the 
madder lake which is then deposited is to be thoroughly 
washed and then dried : it is much denser than that pro- 
duced by the preceding process. In the manufacture of 
alizarin lakes it is customary to introduce a small quantity 
of a preparation known as Turkey-red oil or sulphated 
castor oil. This is made into a soap and added to the 
alkaline solution employed to precipitate the lake. 

By the employment in various proportions of solutions 
of alum and calcium chloride, by the substitution of 
sodium phosphate for the carbonate, and by choosing 
various qualities of madder-root, a number of hues and 



196 MADDER LAKES 

tints of rose and pink madder may be obtained when one 
or other of the methods above described is adopted. The 
oxides of iron, manganese and copper, when used in asso- 
ciation with more or less alumina as a base for receiving 
the various colouring matters of madder, give other hues, 
including madder purple and madder brown. 

But occasionally the pigments sold under these names 
are mixtures. For instance, burnt sienna and copper f erro- 
cyanide have been found in samples of madder brown; the 
presence of copper in madder brown seems, however, to 
be usual, but it arises from the employment of copper 
sulphate in its preparation along with alum. 

From alizarin and from purpurin (either natural or 
artificial) lakes may be readily prepared by dissolving 
these substances in the smallest necessary quantity of an 
alkali, such as ammonia or sodium carbonate, and then 
adding a solution of a pure aluminium salt or some pure 
freshly precipitated and thoroughly washed aluminium 
hydrate. Another and more recent process consists in 
dissolving the colouring matter in a solution of sodium 
aluminate, and then precipitating the * lake ' by adding 
dilute sulphuric acid or, better, a solution of alum. 

The best artificial alizarin of commerce occurs as a 
yellowish powder, presenting the aspect of raw sienna. It 
may, however, be obtained in yellow or orange red crystals, 
either by repeated crystallization from a solvent or by 
sublimation in vacuo. Its colour is always brighter than 
that of purpurin, which in powder has about the hue of 
Venetian red. But when solutions are made of these two 
substances in alkalies, then it is seen that the colours are 
reversed — alizarin yielding a crimson verging upon purple, 
and purpurin a red verging upon crimson. Differences of 
colour will be noticed in the lakes prepared with these two 



ALIZARIN AND PURPURIN 197 

bodies. The directions for preparing pigments from the 
above-named bodies are practically identical with those 
already given in outline, but the minute details of manip- 
ulation can be learned only in actual practice. The 
following process gives an artificial red madder of excel- 
lent hue : Equal weights of pure alum (absolutely free 
from iron and lime) and of the purest artificial purpurin 
in powder are ground together, and then washed with cold 
water until the washings are colourless ; then the residue 
on the filter is boiled with a 5 per cent, solution of pure 
alum, filtered while boiling, and immediately neutralized 
with pure sodium carbonate solution (also boiling) until 
red flocks appear. These are filtered off, and constitute, 
when washed and dried, a fine pigment of a rich red hue. 
By heating the mother liquor to 80°, and adding more 
sodium carbonate, a further and equally good product is 
obtained. The purpurin residue, when again heated with 
more alum-solution and precipitated as above directed, 
yields a further quantity. The final residue, after several 
such exhaustions, produces an impure lake, having a 
brownish-red hue. A very large number of commercial 
preparations of alizarin and of other dye-stuffs closely allied 
to it are now available for the preparation of the so-called 
* madder lakes.' Some of these preparations when dis- 
solved and then precipitated on a suitable basis, yield pig- 
ments of great richness and stability, others, especially 
those which possess a yellow, orange, or red-brown hue, 
are less permanent. Here it may be remarked that, 
broadly speaking, the true or * root ' madders are complex 
so far as their colour-constituents are concerned and 
simple as regards their base, while the converse is true 
of the alizarin lakes. 

Although the madder colours are very much less aft'ected 



198 



MADDER LAKES 



by light than are the pigments derived from cochineal, yet 
it cannot be affirmed that any of them are absolutely per- 
manent when continuously exposed. The following figures 
show approximately the amount and nature of the change, 
observed after certain intervals, in the case of several 
madder pigments used as water-colours : 



Name of Pigment 


Original 

Intensity = lo 


Change of Hue 


♦Madder Carmine, A 


Afte 


r I ; 


y^ear, 


10 - 


Very slight. 


>> )> 


B 




I 




8 - 


Much more purplish. 


" j> 


C 




5 




2 - 




»> j> 


C 




7 




O - 




* 


F 




4 




lO - 


More purplish. 


Madder Red - 


- . 




I 




6 - 


Less red, more blue. 


Rose Madder - 


- - 




I 




8 - 


Slightly more purplish. 


„ B 






2 




3 - 




„ B 






5 




I - 


Smoke grey. 


B 






7 




I - 


Grey. 


*.. „ F 






4 




H ■ 


Slightly more purplish. 


Pink Madder - 






2 




I - 




Purple Madder, 


A - 




I 




7 - 


Duller, less red, more 


5» >J 


C - 




2 




6 - 


More bluish. [blue. 


/> 


D - 




5 




7 - 




fJ .. 


C - 




7 




2 - 




»> 11 


E - 




7 




9 - 


Somewhat puce. 


♦Brown Madder, A 




I 




9 - 


Less red, more yellow. 


j> »i 


B 




2 




I - 


Grey. 


j> » J 


B 




5 




I - 




>> )> 


B 




7 




o - 


Grey. 



The letters A to F indicate different samples of the several 
pigments, which were in all cases ' moist ' colours ; a 
parallel but less complete series with * cake ' colours gave 
practically the same results. The five samples marked * 
are instances of exceptional stability, and are of import- 
ance as showing the possibility of obtaining some, at all 
events, of the madder pigments in a satisfactory form. 
It is noticeable that the paler (pink and rose) madders, 



MINERAL LAKE i99 

which contain much water, are generally more perishable 
than the concentrated madder carmine ; the comparative 
trials having, of course, been made with washes of nearly 
the same depth of tint. 

A study of this table inclines one to think that the 
genuineness and purity of some of these pigments are 
doubtful, yet one specimen only (Madder Carmine C) was 
not tested. In this case the material used was not available 
for analysis, but I have no reason to doubt its authenticity. 

Mineral Lake : Pink-Colotiv — Potters' Pink — Laque 
Minerale — Minerallack. 

Attempts have been made to obtain mineral pigments of 
absolute permanence in order to acquire substitutes for 
the reds and purples of vegetable origin. None of them 
equals in intensity and splendour of colour the derivatives 
of madder. One of the best of these substitutes is mineral 
lake. This compound may be made in many ways. In 
some recipes stannic oxide, chalk and a little potassium 
chromate are directed to be heated together : in one pro- 
cess the operations are begun by precipitating a solution 
of neutral potassium chromate by means of a solution of 
stannic chloride. The precipitate is collected on a filter 
and thoroughly washed. Still moist, it is ground into a 
paste with half its bulk of pure nitre and some stannic 
oxide, and allowed to dry. The dry mixture is projected, 
little by little, into some nitre heated to low redness in a 
crucible. When the basic chromate of tin has settled, the 
nitre, still fused, is poured off. and the residue washed 
thoroughly with water. The product thus obtained 
requires calcination for two hours at a high tempera- 
ture in a luted crucible, in order to develop its colour, 
which much resembles that of almond-blossom when 



200 LIGHT RED 

the matter is finely ground. It appears much richer in 
hue and less opaque when used as an oil-colour. It 
constitutes an unalterable pigment. 

Under the name of Potters' Pink Mr. W. Burton, of 
Pilkington's Tile Works, has introduced to the notice of 
artists a ceramic pigment which is a variety of that which 
has been just described. He says of it that it was 
* invented in Staffordshire by an unknown potter about 
a hundred years ago. It is obtained by calcining a 
mixture of oxide of tin and lime with a mere trace of 
oxide of chromium. It is a semi-opaque colour, unlike 
any usually supplied to artists. It should be particularly 
valuable in paintings in which it is undesirable to use 
madder or alizarin pigments.' It is scarcely necessary 
to add to this account that Potters' Pink is not only a 
permanent pigment which may be used in all methods of 
painting (including fresco), but that it is without action 
on other pigments. 

Light Red: Btiynt Ochre — Rouge Anglais — Brun Rouge 
— Englischvot. 

Light red is, or ought to be, yellow ochre burnt — that is, 
calcined. The different varieties of yellow ochre yield, as 
might be expected, products having various hues and 
tints of this rather pale and dull brownish or orange red. 
Moreover, these hues depend in some measure upon the 
temperature at which the calcination is effected. To 
prepare light red, the selected yellow ochre is usually 
crushed and then roasted on an iron plate heated to red- 
ness. When the desired tint has been attained the 
material is thrown into cold water, ground, and washed. 
Light red may also be made by conducting the finely- 
divided yellow ochre suspended in a current of air into a 



VENETIAN RED 201 

heated chamber or furnace. Light red consists, then, of 
yellow ochre deprived of its water of hydration by means 
of heat. It is necessary to employ yellow ochre as free 
as possible from organic matter and from lime if a bright- 
coloured product be desired. 

Light red possesses a considerable degree of opacity. 
Its hue may be defined as a scarlet, modified by a 
little yellow and grey. It is perfectly permanent and 
without action upon other pigments. 

Light red boiled with hydrochloric acid will, if genuine, 
yield a solution, which after filtration will give no pre- 
cipitate, but merely a slight cloudiness, on the addition 
of a few drops of barium chloride solution. The terms 
' rouge Anglais ' and ' Brun rouge ' are not infrequently 
applied to artificially prepared iron reds. 

Venetian Red : Rouge — Crocus — Colcothar — Caput 
Movtumn Vitvioli — Venetianischrot. 

Originally Venetian red consisted of a native ferric 
oxide or red haematite, less purplish in its tints and 
washes than Indian red. But of recent years the name 
appears to have been transferred to a particular quality of 
artificial ferric oxide, made by calcining green vitriol. 
When this salt is heated in a crucible the upper portion 
of the product, which has been less strongly heated than 
the lower, is of a brighter red than the remainder, and 
after washing and grinding is sold as Venetian red. If 
moistened with a solution of nitre, again heated, and then 
ground and washed, the red tint of the product becomes 
somewhat brighter. 

The hue of Venetian red is less brownish than that of 
light red, and not at all purplish like that of Indian red. 

Venetian red, whether artificial or natural, is a per- 



202 INDIAN RED 

manent pigment which may be mixed with other permanent 
pigments without fear of injuring them ; but it must be 
perfectly free from soluble salts and from any trace of 
sulphates. The presence of the latter may be detected by 
the test described under ' Light Red ' and * Indian Red.' 
But few commercial samples will stand this test, however, 
and we consequently find that many samples of Venetian 
red, owing to the presence therein of sulphates, exert an 
injurious action upon some of the organic pigments used 
as water-colours — notably, upon indigo. 

A very fine native red ochre comes from Tuscany and 
from Krasso in the Banat, Hungary. It is represented 
by the formula 2Fe203, HgO, and goes under the minera- 
logical name of tuvgite. Its hue is that of a fine Venetian 
red : it is probable that the fine native Indian reds and 
red ochres sometimes consist of or contain this hydrated 
ferric oxide, and are not really anhydrous. 

Indian Red : Persian Red — Indian Red Ochre — Indischrot. 

Indian red is a variety of red ochre, or red haematite, 
containing about 95 per cent, of ferric oxide, and having a 
slightly purplish hue. It varies somewhat in quality, and 
often requires sifting through a fine silk sieve, followed by 
washing over, in order to fit it for use as a pigment. Most 
of the Indian red imported from India is a natural pro- 
duct, but some has been prepared by calcination. Some so- 
called Indian red is imported from Ormuz in the Persian 
Gulf; some is an English haematite from the Forest of 
Dean. 

A recent recipe for making an artificial Indian red 
directs that a mixture of 75 parts of green vitriol be taken 
and dried at a moderate heat previous to mixing it wdth 
18 parts of calcined magnesia and 7 parts of common 



INDIAN RED 203 

salt, all the ingredients being in fine powder. The mix- 
ture is then ignited, preferably under reduced pressure, 
and the residuum thoroughly washed with water. By the 
introduction into the original mixture of a little aluminium 
sulphate the purple hue of the product may be enhanced ; 
indeed, it is quite possible in this way to obtain the pig- 
ment known as Mars violet. 

Indian red, when genuine, is a perfectly permanent pig- 
ment in all media, and is without action upon other colours. 
It was extensively employed by the older masters of the 
English Water-Colour School, in association with true 
ultramarine, with Prussian blue, with indigo, or with indigo 
and yellow ochre, to produce the lilac greys of stormy 
clouds. The indigo in some of these greys having often 
perished, the Indian red (and the yellow ochre where 
employed) remains intact, giving a hot and frequently 
foxy red to spaces which were originally cool in hue, and 
comparatively neutral. This change has been incorrectly 
attributed to an action exerted upon the indigo by the 
Indian red. But as indigo disappears when used alone, or 
when a thin wash of it on a sheet of gelatine is placed 
over, but not in contact with, a wash of Indian red, the 
current explanation of the phenomenon in question cannot 
be true. Greys made with light red or Venetian red show 
similar alterations of colour. Colcothar, or jewellers' rouge, 
the red oxide of iron obtained as a residue when green 
vitriol (ferrous sulphate) is calcined, has sometimes been 
called Indian red, and substituted for the native oxide. 
Those portions of the above-named residue which have 
been more strongly heated generally present something of 
the purplish red hue which belongs to the true native 
Indian red. And this peculiar hue may be imparted to 
ordinary rouge by moistening it with a weak solution of 



204 RED OCHRE 

potassium chlorate, drying, and then calcining the mass 
once more. It generally contains basic ferric sulphate, 
and then should be looked upon with suspicion, for it may 
seriously damage the indigo and other organic pigments 
with which it is associated. If a small pinch of Indian 
red be boiled with hydrochloric acid, thrown on a filter, 
and the filtrate tested with barium chloride solution, the 
genuineness of the pigment wdll be proved by the absence 
of any white precipitate of barium sulphate. 

Red Ochre : Red Hmnatite — Red Iron Ore — Scarlet Ochre 
— Red Chalk — Ruddle — Bole — Sinoper — Sittopis — Ruhrica 
— Miltos — Terra Rosa — Arvahida Red — Bolus. 

The pigments above-named are native ferric oxide (or 
iron peroxide) associated with variable proportions of 
mineral impurities such as clay, chalk, and silica. They 
differ from the yellow and brown ochres described on 
page 157, by not containing combined water, in other 
words, the iron to which they owe their colour is ferric 
oxide, not ferric hydrate, except in the case of turgite, 
named on page 202. They occur in very many localities 
accompanying or even constituting some of the most im- 
portant iron ores. Their colour varies with their physical 
state, and with their purity ; some are iron grey, or even 
black, until they are finely ground, when they assume a 
cherry-red hue. Cappadocia yielded to the ancient Greeks 
some at least of their sinopis, or red ochre, but they were 
famihar with the process of calcining yellow ochre in 
order to redden its hue ; and they thus prepared the pig- 
ment to which the name * light red ' is now assigned. 

An unusually bright red variety of haematite from 
Cumberland gave me on analysis, in 100 parts, ferric 
oxide, 947; alumina, 2-0; silica, 2*2, and moisture, i-i. 



INDIAN LAKE 205 

But some almost equally rich red ochres contain much 
less iron oxide, a * sinopis ' from Anatolia, analysed by 
Klaproth, having been found to contain 21 per cent, 
only, and others, from other localities, not above 40. 
The paler varieties of a reddish brown or yellow brown 
hue often consist of mixtures of haematite and yellow 
ochre. A very fine red ochre from Tuscany, the Banat, 
Hungary, and from the Urals, contains about 5 per cent. 
of water, and is considered to belong to a distinct mineral 
species called kirgite, as mentioned before under the 
heading ' Venetian Red.' 

When red chalk (from Hunstanton, Norfolk) is calcined 
at a high temperature it loses its red colour, and becomes 
of a dull olive green hue, a change due in this case to 
the production of calcium ferrite, a compound of lime 
and ferric oxide. 

The terra rosa of Italy owes its pinkish red hue to 
ferric oxide, but it is probably often, if not always, an 
artificial product. 

All the pigments described under the title ' red ochre ' 
are permanent, and without action on other pigments. 

For the substitution of artificially prepared ferric 
oxide, or colcothar, for red ochre, and for the method of 
detecting it, reference should be made to page 202, under 
* Indian red.' 

Indian Lake : Lac Lake — Lack-Lack. 

Lac is a resinous secretion produced by certain plants 
when punctured by the larvae of the Coccus lacca, an 
East Indian hemipterous insect. Amongst the trees 
which the insect chiefly attacks are Butea frondosa, Ficus 
religiosa, and F. hengalensis, Schleichera tvijuga, Shorea 
robusta, and Ztzyphus jujuha. The lac, though a secretion 



2o6 INDIAN LAKE 

primarily derived from the tree on which the insects 
feed, is yet profoundly modified, particularly with respect 
to its colour, during its passage through the animal's 
body. It varies in colour with the species of tree, but 
always consists mainly of three substances— namely, a 
resin, a colouring matter, and a wax. The resin, which 
constitutes two-thirds of the substance, is obtained in the 
form known as ' seed-lac ' by pounding in water the lac 
which has been removed by pressing with a roller the 
encrusted twigs on a floor. The water becomes red ; 
from it, by evaporation, the crude < lac-dye ' is obtained. 
This is made into cakes, and dried. 

The lac-dye of commerce contains nitrogenous and 
mineral matters, as well as several dark-coloured 
impurities, and some resin. In order to prepare a lake 
from it, it should be first powdered, and then digested in 
spirit of turpentine, or benzene. The purified residue 
is, when dry, extracted with sodium carbonate solution : 
the liquor is afterwards filtered and precipitated with 
alum solution. The precipitate thus formed is washed 
and dried in the dark. 

Indian lake was used by the Venetian and Flemish 
painters of the sixteenth century, but it does not seem, 
so far as one can gather from the notices of it in the 
work of De Mayerne, and in the Secreet-Boeck, to have 
been often obtained of good colour. It is even spoken 
of as a ' light brown.' 

Indian lake is inferior in beauty, and in variety of 
hues, to the colours from madder ; it is also more affected 
by light. But it is distinctly less fugitive than crimson 
lake and the other cochineal pigments. 

I do not know from direct experiment whether the com- 
parative stability of the red colouring matter from kermes 



COCHINEAL LAKES 207 

when used as a dye for animal fibres belongs also to all 
the lakes prepared from this substance : anyhow, kermes 
pigments are, so far as I can learn, not met with in com- 
merce at the present time. Their use in European paint- 
ing seems to have been displaced, first of all by Indian 
lac lakes, and then by cochineal lakes. The colouring 
matters produced by these three kinds of coccus are 
closely allied chemically. 

Carmine and the Cochineal Lakes : Carmin—Laque 
Cramoisie, or Crimson Lake — Purple Lake, etc. — Karmin. 

Cochineal consists of the dried wingless females of a 
species of coccus (C. cacti) which feeds upon several kinds 
of Opimtia, or cactus. The best quality comes from Tene- 
riffe, and contains about half its weight of colouring 
matter. This colouring matter is a glucoside, to which 
the name of carminic acid has been given. When this 
substance is treated with weak sulphuric acid, it is 
resolved into a sugar and another colouring matter called 
carmine red. 

The carmine of commerce is prepared directly from 
cochineal, and is the most concentrated and purest form of 
any of the pigments derived from this source. The 
methods of preparation differ, but in all the colouring 
matter is extracted from the insects by means of boiling 
water, with the subsequent addition of small quantities of 
alum, or nitre, or potassium oxalate, or cream of tartar ; 
occasionally a small quantity of stannous chloride is em- 
ployed also. The liquor, after a repose of some days or 
even weeks, deposits a great part of the colouring matter 
as a deep crimson-red powder, which is then thrown on a 
filter, washed and dried in the dark. However prepared, 
it contains fat, albuminoid matter, mineral salts, and 



2o8 COCHINEAL LAKES 

other impurities ; the finest varieties, however, dissolve 
perfectly in strong liquor ammonise. The liquor, which 
has deposited the carmine, gives up the remainder of its 
colouring matter to freshly - precipitated aluminium 
hydrate, or, after having been rendered alkaline by 
potassium carbonate, to a solution of alum. Lakes are 
thus formed. Lakes are also made by directly precipi- 
tating cochineal extract with solutions of potassium car- 
bonate and alum. A purplish tinge is given to the product 
by a small quantity of lime ; other hues, generally dull, 
are imparted by the presence of iron, manganese, or 
copper in the solutions employed. The cochineal lakes 
always contain a larger quantity of water and of alumina 
(or other mineral basis) than carmine, and are conse- 
quently weaker. Scarlet lake is usually a mere mixture 
of crimson lake and vermilion, but alizarin lake may 
replace the former. 

Beautiful and rich as are the colours prepared from 
cochineal, not one of them should ever find a place upon 
the palette of the artist. They all become brownish, and 
ultimately almost disappear after a short exposure to 
sunlight or the more prolonged attack of strong diffused 
daylight. In six hours of sunshine a strong wash of fine 
crimson lake on Whatman paper lost 8 per cent, of its 
original intensity ; this was on April 12. The loss during 
a second period of six hours' exposure was much less, but 
after the lapse of four months less than 5 per cent, of the 
original colour remained. In the case of carmine, from 
one to two years was required for the complete oblitera- 
tion of every trace of the original crimson from a deep 
wash of this pigment. All the cochineal pigments be- 
come somewhat brownish during the course of fading, 
but ultimately, when all the red has disappeared, either 



BURNT CARMINE 209 

a greenish-grey or a faint sepia-like brown is the sole 
residue. 

The term 'lake' belongs to all colouring-matters 
throv/n down upon such a basis as alumina ; but when 
purple, crimson, or scarlet is prefixed to the word lake, 
cochineal colours are always understood. So carmine used 
alone refers to cochineal carmine, although it is a general 
term for a group of rich pigments, of which madder car- 
mine and indigo carmine are perfectly distinct examples, 
derived from madder and indigo respectively. 

It is not necessary to say more about the various 
cochineal pigments, nor to point out their many falsifica- 
tions, for their value as artists' colours is very small. No 
artist who cares for his work and hopes for its permanency 
should employ them. 

Burnt Carmine. 

This preparation should rather be called ' roasted car- 
mine.' It is obtained by carefully heating the carmine 
made from cochineal. It possesses a beautiful hue, but 
is quite as fugitive as the product which yields it. Two 
years' exposure to sunlight completely destroyed a strong 
wash of cake-burnt carmine on paper. The moist pig- 
ment had lost nine-tenths of its intensity at the end of 
the same period, while the small residual proportion of 
the colour had suffered no further change in depth at the 
end of a further lapse of three years. Burnt carmine is 
rather less fugitive in oil than in water colour. Experi- 
ments in the latter medium gave, after exposure to 
sunlight, the following residual intensities out of ten : 

Moist, after two years ... ... i 

Cake, after two years ... ... o 

Moist, after five years ... ... i 

14 



210 RED LEAD 

A sample of burnt carmine purchased of Messrs. New- 
man about the year 1815 was found (as might have been 
anticipated) to have retained its colour in the cake per- 
fectly to the present year ; but a wash of it on paper 
possessed no greater nor less degree of permanency than 
a wash of the same pigment prepared by the same 
makers in 1886. 

Red Lead : Minium — Saturnine — Mijte Rouge, Mine 
Orange — Mennige — Rosso Satimio . 

This beautiful orange-red pigment approaches in com- 
position a compound of two molecules of protoxide of lead 
with one molecule of binoxide, and may be approximately 
represented by the formula Vhfi^. The paler and more 
orange-tinted varieties contain an excess of protoxide of 
lead, often accompanied by a little carbonate. 

This pigment is peculiarly liable to discoloration in the 
presence of sulphuretted hydrogen : it acts energetically 
upon some paints, on the cadmium yellows, for example. 
It is quite inadmissible as a water-colour, and cannot be 
considered as safe in oil. 

Cobalt Red : Rose de Cobalt — Cobalt Violet — Kobaltrot. 

This little-used pigment should consist of the oxides of 
magnesium and cobalt. It is prepared at a high tempera- 
ture and is quite permanent. One method of making 
this pigment involves the use of magnesium carbonate or 
oxide, which is made into a paste with a solution of pure 
cobalt nitrate. This paste is then slowly dried, and ulti- 
mately calcined in a crucible. Different preparations of 
this pigment differ considerably in hue ; a purplish cast 
is sometimes due to the accidental presence of alumina. 



COBALT RED 211 

Pigments consisting of cobalt arseniate are occasionally 
called ' cobalt red ' ; the term ' cobalt violet ' is usually 
and may be more fitly applied to them. The hue they 
present is rather bluer (or less red) than that of the 
flowers of the common foxglove. Cobalt violet has been 
made from the mineral known as erythrite, or cobalt- 
bloom, which has the formula CogAsgOg, SHgO ; an 
artificial cobalt arseniate is also made by oxidizing cobalt 
sulph-arsenide, which is first reduced to powder and then 
roasted with twice its weight of potassium carbonate. 
After further treatment, the final product obtained by 
grinding and washing constitutes a pigment of a rather 
coarse grain which does not work smoothly as a water- 
colour, but has the advantage of complete stability in all 
vehicles. A sample of this cobalt violet of good quality 
was found to contain no water and to suffer no change 
when heated to a red heat in the air ; along with cobalt 
arseniate it contained some phosphate. 



CHAPTER XVI 

GREEN PIGMENTS 

Terre Verte : Green Earth — Tevre de Verone — Gvilne 
Erde — Terra Verde. 

There are two rather indefinite minerals, probably not 
really distinct — namely, glauconite and celadonite — which 
furnish the raw material from which the artists' pigment, 
generally known as terre verte, is prepared. The form, 
or variety, celadonite is the rarer of the two : it is softer 
than glauconite : both minerals are probably mixtures. 
Green earth of very good quality is found at Bentonico, 
to the north of Monte Baldo, near Verona, where it occurs 
in cavities in an amygdaloid rock. The best samples 
possess a deep olive-green colour ; inferior specimens are 
celandine or apple-green. Green earth is obtained from 
a large number of European and American localities, and 
varies much in chemical composition. From its greenish 
hue it has been assumed to consist chiefly of a ferrous 
silicate — that is, a silicate of protoxide of iron, and in this 
way it is represented in the older analyses. But more 
exact analyses have shov/n that green earth contains but 
a small part of its iron in the protoxide condition, and that 
it is mainly a ferric silicate. A choice specimen of fine 
hue from Monte Baldo gave the following results on 
analysis, the numbers representing parts in one hundred: 



TERRE VERTE 213 



Water, given off at 100° C. 4*1 


Lime - 


- 


- 


- i-i 


Water, given off at a red heat 42 


1 Magnesia - 


- 


- 


- 5-6 


Ferric oxide (Fe.^O.^) - 20 3 


Potash 


- 


- 


- 6-4 


Ferrous oxide (FeO) - - 26 


Soda - 


- 


- 


- 2-3 


Alumina - - - - 17 


Silica 




- 


- 517 



Green earth is thus allied to the hornblendes, differing 
mainly in the partial replacement of soda by potash and in 
the presence of water. Being itself an alteration-product, 
it is not likely to be amenable to further change, particu- 
larly as the iron in it is for the most part fully oxidized. 

Terre verte occurs in ancient Roman wall-paintings (the 
prepared pigment was found in the ruins of Pompeii), and 
was largely employed by the early artists of Italy in their 
works in tempera, fresco, and oil. But amongst the green 
pigments found in ancient wall-paintings in Rome and 
Pompeii there occurs also a substance of a richer and 
deeper hue than that possessed by terre verte. It was 
made by grinding into fine powder a kind of green jasper ; 
it has proved quite permanent. 

Terre verte is prepared by carefully selecting the richest- 
coloured and most uniform specimens of the mineral, 
grinding them to fine powder, and washing the pulverized 
material with rain-water ; it is then dried. Sometimes the 
selected fragments are heated, and then quenched in very 
dilute hydrochloric acid to remove ochre and other im- 
purities ; the undissolved portion is then ground, washed 
thoroughly, and dried. Most samples of terre verte are 
found to be perfectly stable both in water-colour and oil- 
painting. It is a semi-opaque or translucent pigment, 
without much body in oil. It has no action on, nor is it 
affected by, other permanent pigments. When used in 
oil or tempera as a ground-colour or in the under-painting, 
terre verte sometimes becomes more conspicuous in the 



214 GREEN OXIDE OF CHROMIUM 

course of time, owing partly to the deepening of its own 
hue and partly to the increased translucency of the pig- 
ments which have been laid over it. Some samples of 
terra verte seem to be liable to become sHghtly rusty 
when brought into contact with lime hydrate in true 
fresco painting. This is probably due to the further 
oxidation of some of the ferrous oxide they contain. Cal- 
cined terre verte is known as Verona brown. 

Terre verte is rarely adulterated. A pure sample is not 
affected when drenched with liquor ammoniae, becoming 
neither more bluish (presence of copper compounds), nor 
more brownish (presence of Prussian blue). But although 
adulterated terre verte is rarely met with I have found that 
a well-known firm of artists' colourmen sell, or have sold, 
a mixture with green ultramarine under the name of 
terre verte. Tubes of oil-colour of this sort have been 
submitted to me for analysis. This substitution is unfair 
to the artist, who has a right to obtain the material he 
demands. Green ultramarine freed from oil gives sul- 
phuretted hydrogen when moistened with hydrochloric 
acid, which has no such action on terre verte. 

Green Oxide of Chromium: Chromium Sesquioxide — 
Tnie Chrome Green — Opaque Oxide of Chromium — Vert 
de Chrome — Griines Chromoxyd, 

The so-called native oxide of chromium, or chrome 
ochre, is a mere greenish clay, containing not more than 
lo per cent, of chromium oxide. But another mineral 
(from Okhansk, in Siberia) is of a deeper green, and 
sometimes contains one-third of its weight of this oxide. 
We are not aware that any attempt to employ these 
minerals as pigments has ever been made. 

The green oxide of chromium, CrjOg, varies in hue, in 



GREEN OXIDE OF CHROMIUM 215 

depth of colour, and in opacity according to the process 
of its preparation. It may be made either in the ' dry ' 
way or the ' wet ' way. Perhaps the finest quality is that 
produced by heating mercurous chromate in a retort till 
the whole of the mercury has been distilled off. This is 
an expensive process, but the product is excellent in colour 
and body. Ammonium bichromate gently heated, in small 
portions at a time, yields a dull-coloured but a useful 
variety of this pigment ; but there is a similar, though more 
economical process, yielding a better-coloured product. 
This consists in gently heating together and then calcining 
a mixture of 3 parts of neutral potassium chromate with 
2 parts of ammonium chloride. The mass is to be 
thoroughly washed with hot water, dried, and again ignited. 
Two other processes for preparing this pigment in the dry 
way may be commended. In both of them potassium 
bichromate (free from iron) is used, but in the one case 
sulphur, in the other starch, is employed, in order to effect 
the reduction of the chromic salt to the condition of ses- 
quioxide. The sulphur method yields at once a good pig- 
ment, which needs nothing but a thorough washing, first 
with very dilute sulphuric acid and then with water, fol- 
lowed by grinding, to fit it for use, but a second calcination 
is required in the starch process. In order to prepare 
oxide of chromium by the wet way, a solution of an 
alkaline chromate or bichromate is to be reduced by 
sulphur or other reducing agents, or a sesquisalt of 
chromium is precipitated by ammonia or a fixed alkali. 
The hydrated sesquioxide is thrown down ; after having 
been washed, this substance is gently calcined. The 
hydrate itself, when air-dried, constitutes one of the forms 
of ' transparent oxide of chromium.' 

The ordinary or opaque oxide of chromium usually 



2i6 VI RID I AN 

occuis in the form of a greyish-green powder of consider- 
able body. It is quite permanent under all conditions of 
exposure and of commixture with other pigments, and is 
available in all the processes of painting. Its tints with 
flake-white, and the yellowish greens which it yields 
with aureolin, are peculiarly valuable to the landscape- 
painter. 

Green oxide of chromium is rather imitated than adul- 
terated. This pigment when genuine is not altered in 
colour either by ammonium sulphide or caustic potash. 
But under the name of chrome-green mixtures of Prussian 
blue and lead chromate are constantly sold. These prep- 
arations generally contain some barium sulphate, often a 
considerable quantity of gypsum, and, occasionally, alu- 
mina. The term 'chrome-green' cannot be justly applied 
to these mixtures, which are greatly inferior in stability 
to the pigments under discussion, and are all discoloured 
by lime and alkalies. 

ViRiDiAN : Emerald Oxide of Chromhim — Vert Pannetiev — 
Vert de Guignet — Vert Emeraude — Mittler's Green — 
Feuriges Chvomoxyd. 

About the year 1838 Pannetier and Binet began to make 
a beautiful chromium green by means of a secret method. 
Many years afterwards M. Guignet discovered and 
patented a process by which this admirable pigment 
could be manufactured. About 8 parts of crystallized 
boracic acid and 3 parts of potassium, bichromate are 
thoroughly mixed and calcined. The mass obtained is 
treated with cold water, washed by decantation, ground 
wet, washed with hot water, and carefully dried. The 
product is a hydrated chromium sesquioxide, in which a 
variable amount of the boracic constituent is often re- 



VIRIDIAN 217 

tained. Viridian is, however, essentially a hydrated ses- 
quioxide of chromium, having the formula CrgOg, 2H2O. 
In the preparation of this pigment it often happens that 
sufficient care is not taken to wash it perfectly free from 
all soluble salts. I have known the metal tubes in which 
this moist water-colour has been kept to be corroded by 
these salts and to fall to pieces in a few months. The 
presence of such saline matter is easily detected by mixing 
the moist or cake colour with water and noting if coagu- 
lation or curdling takes place. 

It would be difficult to exaggerate the value of this ad- 
dition to the artist's palette. The colour of viridian is a 
very deep bluish green of great purity and transparency. 
It furnishes, with aureolin on the one hand and with ultra- 
marine on the other, an immense number of beautiful hues, 
adapted to represent the colours of vegetation and of water. 
It is quite unaffected by sunlight and sulphuretted hydro- 
gen, and it has no action on other pigments. Moreover, 
it may be safely used with all the different painting media, 
and upon all kinds of painting-grounds. 

Viridian is the name by which this pigment is perhaps 
now best known in England. It is unfortunate that it 
should be called ' Vert Emeraude ' in France, since it has 
little in common with the poisonous emerald green of our 
colourmen. This pigment is sometimes adulterated with 
baryta yellow in order to modify its hue. This substance 
may be readily detected by moistening the pigment with 
dilute hydrochloric acid, when a yellow solution is ob- 
tained. 

Arnaudon's chrome green is of a somewhat opaque 
green hue, rather like that of Schweinfurt ; it is a phos- 
phate of chromium. A similar product is Mathieu-Plessy's 
chrome green ; but under the name of ' chrome green,' 



2i8 COBALT GREEN 

'green cinnabar' and 'griiner Zinnober,' spurious pig- 
ments are constantly sold, the commonest of them con- 
sisting of mixtures of chrome yellow and Prussian blue. 
They are worthless in comparison with viridian. 

A clear and bright green called ' vernalis' is one of the 
potters' pigments introduced to the notice of artists by 
Mr. Wm. Burton. It is formed at a very high tempera- 
ture and is perfectly permanent. It contains lime but 
owes its colour to chromium. 

Cobalt Green : Rinmann's Green — Vert de Cobalt — Vert 
de Zinc — Kohaltgriin . 

It has long been known that the oxide or a salt of zinc, 
moistened with a solution of cobalt nitrate, and then 
strongly heated before the blow-pipe, gives a porous mass 
of a beautiful green hue. This compound or mixture of 
the oxides of zinc and cobalt may be prepared by : (i) Pre- 
cipitating with an alkaline carbonate a mixture of the 
nitrates of cobalt and of zinc, and then strongly heating 
(after washing) the precipitate formed ; (2) Making a paste 
of zinc oxide and water, and adding to it a solution of 
nitrate or sulphate of cobalt, or of roseo-cobaltic chloride ; 
the mass is then dried, calcined at a dull red heat, thrown 
into water, ground, washed, and dried. Method No. 2 
gives a finely coloured product, the depth of hue being 
proportional to the percentage of cobalt oxide. If the 
latter oxide amount to one-third of that of zinc the colour 
is a very deep bluish green ; with no more than one-sixth 
the colour is still rich. Some specimens do not contain 
more than one-twentieth — sometimes even less — of cobalt 
oxide, and yet they are far from pale. An excellent deep 
sample contained 12 per cent, of cobalt oxide. 

When properly prepared, cobalt green is a pigment of 



EMERALD GREEN 219 

great beauty and power.* The deeper tones of cobalt 
green are almost transparent in oil. The pigment works 
well, is quite permanent, and has no action on other pig- 
ments. Cobalt green is, in fact, one of the too-rare pigments 
which is at once chemically and artistically perfect ; such 
at least is the conclusion I reached from my own trials, 
but Mr. J. Scott Taylor tells me that cobalt green fades a 
good deal when exposed to damp, although it stands light 
well. It must be admitted, however, that it may be 
exactly imitated by a mixture of viridian and artificial 
ultramarine with a little zinc white. 

Cobalt green is again coming into artistic use, as it is 
equally adapted for all the methods of painting. It \vas 
discredited for awhile by the inferiority of the product 
obtained by Rinmann's original process (No. i above). It 
ought not to be an expensive pigment. 

Sometimes cobalt green is prepared by precipitating a 
cobalt salt with an alkaUne arseniate or phosphate, and 
then heating the precipitate with zinc white. 

Emerald Green : Cupvic Aceto-Arsenite — Schweinfuvt 
Green — Vert Paul Veronese — Schweinfurter Gri'in. 

This pigment was discovered in 1814 during the course 
of experiments made wdth the object of preparing an im- 
proved Scheele's green. It may be prepared by half a 
dozen slightly differing processes, but in all verdigris (or 
vinegar and blue vitriol) and white arsenic are the two 
essential materials employed. Generally verdigris is dis- 
solved in acetic acid, and added to a boiling aqueous 

* One sample of deep transparent cobalt green which I obtained 
from a Paris colour-manufacturer contained both viridian and 
ultramarine, added to enrich the colour of the cobalt green which 
formed the basis of the pigment. 



220 EMERALD GREEN 

solution of white arsenic : on continued ebullition a de- 
posit of emerald green occurs. Sometimes copper sul- 
phate, potassmm arsenite, and acetic acid are employed. 
Whatever the method, it is necessary that the coloured 
product be washed with boiling water to remove the last 
traces of soluble salts. 

The hue of this pigment is a nearly normal green, slightly 
verging upon bluish green ; it is brighter and more opaque 
than Scheele's green, and, like it, is a deadly poison. It is 
less attacked by sulphuretted hydrogen than Scheele's 
green, but as a water-colour, does not long remain untar- 
nished in impure air. In oil it is practically permanent, 
both alone and when used with the majority of permanent 
pigments. It is, however, quickly blackened by the cad- 
mium yellows. Emerald green cannot be relied upon as 
permanent in fresco and tempera painting. Its use in 
wall papers and in the decoration of all domestic furniture 
and fabrics is to be deprecated, by reason of its poisonous 
character ; but is, happily, at the present time, in great 
measure abandoned. 

Emerald green, if pure, dissolves perfectly in boiling 
dilute nitric or hydrochloric acid ; the solutions thus 
made should yield no precipitate with a few drops of 
barium chloride solution. An undissolved residue gener- 
ally shows the presence of baryta white. 

Emerald green may be distinguished from Scheele's 
green by a simple experiment. If a small pinch of the 
dry powder be warmed with a few drops of moderately 
strong sulphuric acid (half oil of vitriol, half water), acid 
vapours, having the smell of vinegar, will be given off only 
when true emerald green is the subject of the experiment. 

On the Continent, Vert Emeraude is the name given to 
viridian, the emerald oxide of chromium. 



SCHEELE'S GREEN 221 

Scheele's Green : Cttpric Arsenite — Swedish Green — 
Mitis Green — Scheeles Gn'in. 

This pigment, discovered in 1778, is an arsenite of cop- 
per with an excess of copper oxide. It is best prepared by 
dissolving, in separate portions of hot water, white arsenic 
and blue vitriol. The solutions are then mixed, and to the 
mixture is added, in small successive portions, a solution 
of potassium carbonate. These additions are stopped when 
the precipitated pigment has attained its maximum of 
colour intensity. In another process, a hot solution of 
potassium arsenite is added to a hot solution of blue 
vitriol. This pigment needs thorough washing with hot 
water, and must be dried at a moderate temperature. 

Scheele's green presents nearly the same characteristics 
as emerald green, but is in every way inferior to that 
pigment. It is eminently poisonous. It should not find 
a place on the palette of the artist. 

Vienna green, Mitis green, and Veronese green are 
names which have been given to specially prepared 
varieties of this cupric arsenite ; but there are very many 
other designations by which pigments of essentially the 
same composition are known. They are prepared by 
slightly modified processes, and frequently contain such 
foreign matters as chalk, heavy spar, or gypsum. 

Malachite : Green Verditer — Green Bice — Mountain Green 
— Green Carbonate of Copper — Vert de Montagne — Berg- 
griin — Malachitgriin. 

This green copper mineral was employed as a paint by 
the ancients. It often accompanies the blue carbonate, 
and occurs in many European, Asiatic, African, and 



222 MALACHITE 

American localities. The mines at Ekaterinburg and 
Nischne Tagilsk in Russia, and at Burra-Burra in South 
Australia, furnish malachite of fine colour ; it also occurs 
abundantly in Namaqualand. Its variations in depth of 
colour are due less to impurities than to differences in its 
state of aggregation. Its specific gravity is about 4. Its 
composition is that of a hydrate and carbonate of copper. 
It may be represented by the formula CuCOgjCuHgOg. It 
contains, therefore, less of the copper carbonate than 
azurite, or blue verditer. 

Malachite requires no other treatment than careful 
grinding to fit it for use as an artists' pigment. The raw- 
material must, however, be carefully selected, and all 
visible impurities, such as ochreous veins and deposits, 
and azurite, completely removed. An artificial malachite 
was prepared and largely used in the seventeenth century, 
and is still often substituted for the mineral ; but it is in- 
ferior in colour and stabiHty to the native form. 

Malachite as an oil-paint has often proved to be per- 
manent, although it may seem to acquire a dull, brownish 
hue, owing to the darkening and yellowing of the oil ; 
sometimes, however, it becomes somewhat olive in 
colour. In admixture with cadmium yellow it is liable to 
blacken. It is so easily injured by impure air when un- 
protected by any hydrofuge, that it is quite inadmissible 
as a water-colour. In old tempera paintings it is some- 
times found to have stood well ; but the sulphur from 
the egg-medium and from the size has not infrequently 
browned it. 

Malachite is sometimes adulterated with baryta white ; 
sometimes a mixture of that pigment and an arsenical 
green is substituted for it. The former falsification may 
be detected by boiling the sample in hydrochloric acid. 



VERDIGRIS 223 

when the malachite dissolves, leaving the baryta white 
as a sediment. To detect an arsenical green, a small 
portion of the sample should be mixed with powdered 
charcoal, gently warmed at first in a long narrow test- 
tube to drive off moisture, and then strongly heated ; a 
dark sublimate of metalhc arsenic will form on the cooler 
part of the tube. 

Verdigris : Basic Copper Acetate — Vevt-de-Gris — Verdet 
de Montpelliev — Gvilnspan. 

This green copper pigment was called by the writers 
of the fourteenth century 'viride Graecum,' or, more 
simply, * viride,' ' viride terrestre ' being used for green- 
earth — that is, 'terre verte.' * Vert-de-Grece ' — that is, 
verdigris — was used by the ancient Romans as a pig- 
ment, and has been detected in the wall-paintings of 
Pompeii. It occurs in early Italian tempera pictures ; 
but it has frequently injured the gesso-ground on which 
it has been laid, forming calcium acetate with the calcium 
carbonate, and disintegrating the surface. The blackness 
of the shaded parts in many Venetian and Spanish pictures 
of the sixteenth and seventeenth centuries has been attri- 
buted to the changes which this pigment suffers in oil. 
The medieval writers on the practice of painting en- 
deavoured to show how the peculiar liability of verdigris 
to change could be obviated by locking it up in some 
hydrofuge substance, such as a resin or balsam. But the 
problem actually possesses little practical interest to-day, 
though of real moment in the study of old pictures. In 
the modern palette the place of verdigris is taken by per- 
manent greens derived from chromium and from cobalt : 
concerning the safety of these we need not be anxious. 
The large proportion of resinous matter employed by 



224 VERDIGRIS 

early painters for the protection of verdigris from alter- 
ation, and the success of this precautionary measure, 
may be seen in the green drapery in several pictures by 
Van Eyck and Mabuse in the National Gallery and at 
Hampton Court. It should, however, be stated that the 
older processes for preparing verdigris often yielded a 
product much more alterable in the presence of damp 
than is the verdigris which for a century or more has 
been made at Montpellier. 

Verdigris is commonly called in chemical language a 
basic acetate of copper. In fact, it is a mixture of three 
such acetates, its varying hues, ranging from green to 
greenish blue, being dependent upon the relative pro- 
portions of these acetates. The most blue basic acetate 
contains i molecule of copper acetate, and i of copper 
hydrate, with 5 molecules of water ; the greenest has 
twice as much acetate. Average verdigris contains in 
100 parts about 29 parts of anhydrous acetic acid, 43 of 
copper oxide, and 27 of water. It is nearly insoluble in 
cold water ; but by continuous washing, or by continuous 
exposure to moist air, is ultimately decomposed. 

The Montpellier process for making verdigris consists 
in exposing thin strips of metallic copper to the vapours 
arising from grape marc undergoing the acetic fermenta- 
tion. The operation is conducted in a moist, warm 
atmosphere ; finally, the whole substance of the metallic 
copper is transformed into verdigris. 

An impure atmosphere containing sulphuretted hydro- 
gen blackens verdigris; it is also affected by moisture 
and by carbonic acid. As a water-colour, it is quite 
inadmissible ; in oil, it stands pretty well if ' locked up ' 
in the way already described. But it acts energetically 
upon several important pigments, and is very poisonous. 



VERDIGRIS 225 

For these reasons its employment in artistic painting 
ought to be abandoned. 

Verdigris, if pure, dissolves perfectly in liquor ammoniae, 
any gypsum or barytes present as diluents or adulterants 
remaining undissolved. If blue vitriol has been added to 
verdigris, it also will dissolve in the ammonia ; but this 
falsification may be detected by acidifying the ammoniacal 
solution with hydrochloric acid, and then adding solution 
of barium chloride — a white precipitate of barium sul- 
phate indicates the presence of copper sulphate. 

There are many composite green pigments sold by 
artists' colourmen ; none is of real value. Green lake, a 
mixture of quercitron lake and Prussian blue ; Hooker's 
green — gamboge and Prussian blue ; olive green — Indian 
yellow, umber and indigo ; and olive lake, a mixture of 
quercitron lake, bone brown and ultramarine — all these 
belong to the same category. However, there is one 
mixed pigment, the so-called ' Cadmium-green ' on which 
a favourable judgment may be passed : it consists of 
viridian and cadmium yellow. 



15 



CHAPTER XVII 

BLUE PIGMENTS 

Ultramarine: Lapis Lazuli Blau — Lasuvstein Blau — 
Outremer — Bleu d'Aziir. 

There are at least three mineral species, closely allied in 
chemical composition, and generally presenting a more or 
less marked blue colour, which contain as their essential 
constituents the five elements, silicon, aluminium, sodium, 
sulphur, and oxygen, and which owe their characteristic 
hue to the same compound. From one of these minerals, a 
variety of ' hauyne,' often called ' lapis-lazuli,' the true or 
native ultramarine is obtained. This stone occurs, of very 
varying purity and colour, at Bucherei,Transbaikal,andin 
many other Siberian localities ; at Ditro, in Transylvania ; 
in the Andes of Ovalla, Rio Grande ; and in several regions 
of Persia, Tibet, and China. It is the ' sapphire ' of ancient 
authors. Small golden specks of iron-pyrites are frequently 
irregularly scattered through its substance ; it is also very 
frequently associated intimately with portions of the rocky 
gangue, or matrix (limestone, syenite, granite, etc.), in 
which it occurs. Very fine lapis-lazuli comes from Tibet. 
To prepare a pigment from this mineral, selected pieces 
of small size, as free as possible from pyrites or other im- 
purities, are heated in a crucible and quenched (etonne) 
in cold water, or very weak vinegar. The material, thus 

226 



ULTRAMARINE 227 

disintegrated, is washed by decantation, and then dried 
and carefully ground. The powder is then purified by 
elutriation, or ' washing over,' the several wash-waters 
depositing pigments of different depths of colour, and of 
different degrees of fineness. Some manufacturers adopt 
an old process, and make the powder into a soft mass with 
a little rosin, linseed oil and beeswax, and knead, beat, or 
macerate the lump, secured in a bag of coarse muslin 
under very weak potash, or soda-lye — the alkaline water 
carries off or withdraws the greater part of the pigment, 
and deposits it on standing. The richness of the blue 
product obtained depends primarily upon the original 
quality of the stone, but several grades are always pro- 
curable from the same raw material by means of the 
above-described processes, bluish-grey and grey powders, 
known respectively as ultramarine ash and mineral grey, 
being the last and the least valuable products, while the 
deepest and finest pigments are deposited from the 
earliest wash-waters. 

Optically, the superb blue of native ultramarine ap- 
proaches more closely than the blue of any other pigment 
to the pure normal blue of the solar spectrum ; it shows 
very little violet and in this respect is unlike most speci- 
mens of artificial ultramarine. Ultramarine is somewhat 
harsh and granular in texture, a characteristic which may 
be reduced by a small admixture of Chinese white, but 
which becomes more marked when it is used as a light 
wash, or in conjunction with transparent pigments, in 
water-colour painting. It more nearly approaches trans- 
parency when used in oil, and is then of excellent working 
quality. 

It is generally considered that ultramarine withstands 
the action of light, moisture and sulphuretted hydrogen 



228 ULTRAMARINE 

perfectly, and that it neither affects nor is affected by any 
other pigments. I have, however, been informed by an 
English landscape-painter in oil, who has largely employed 
native ultramarine in the skies of his pictures, that he has 
lost faith in its inalterability. But the question arises, 
' Was the pigment used always authentic ?' It dries well 
in oil. It is decolourized at once by a hot solution of 
alum, and ultimately even by a saturated cold solution, 
which, however, bleaches very quickly all but the most 
stable varieties of the artificial pigment. All mineral 
acids, save carbonic, and all the common organic acids, 
such as acetic, oxalic and citric, discharge the colour of 
native ultramarine. It is only by a combination of 
several tests in the hands of a skilled chemist that the 
discrimination of genuine from spurious ultramarine may 
be with certainty accomplished. 

It may, however, be mentioned here that when a current 
of hydrogen gas is passed over true ultram.arine heated in 
a glass tube the powder retains its colour wholly or par- 
tially for an hour or more, while the best artificial pig- 
ment similarly treated becomes grey or greenish grey. 

In the works — both in fresco and tempera, and in oil — 
of many of the old masters, and in a large number of 
illuminated manuscripts, the permanence of true ultra- 
marine may be seen. If in some cases it has acquired a 
greenish or dull hue in oil-painting, such change is due to 
the yellowing of the oil and varnish, and not to any 
deterioration of the pigment. 

The price of genuine ultramarine is very high. This 
is due less to the scarcity of the original lapis-lazuli from 
which it is derived, than to the small yield and to the 
elaborate and tedious operation by means of which the 
pigment is prepared. But when every allowance is made 



ARTIFICIAL ULTRAMARINE 229 

on account of the troublesome and lengthy process of 
manufacture, the cost of ultramarine is unwarrantably 
excessive. 

Artificial Ultramarine: New Blue — French Blue — 
Permanent BUie — Gmelin's Blue — Guimefs Blue — Kiinst- 
liches Ultramarin. 

In the year 1814 a blue coloration, subsequently proved 
to be due to ultramarine, was noticed in the soda (black- 
ash) furnaces of St. Gobain. About fourteen years after- 
wards a method of making the same blue substance at will 
was discovered by Christian Gmelin, and by Guimet ; this 
method was founded in part upon chemical analyses of 
natural ultramarine, and in part upon a study of the con- 
ditions under which the above-named blue coloration 
occurred. By successive improvements in its manufac- 
ture artificial ultramarine is now produced at a cost of no 
more than a few pence per pound. It is chiefly made in 
Germany and in France. 

The raw materials employed in the preparation of ultra- 
marine are kaolin, or China-clay, silica, sodium sulphate, 
sodium carbonate, sulphur, charcoal and rosin. Some 
makers omit the sodium sulphate, others the rosin, while 
calcined alum is occasionally substituted for the kaolin. 
These materials are heated together in closed crucibles in 
a furnace, and slowly cooled. A greenish porous cake is 
the product: this is powdered and gently roasted, after the 
addition of a little sulphur, for some hours. The material 
is again powdered, and then washed and dried : further 
calcination is sometimes required to develop the proper 
blue colour. 

In preparing artificial ultramarine for use as an artists' 
pigment it must be very finely ground, and very thoroughly 



230 ARTIFICIAL ULTRAMARINE 

washed with water free from lime. The grinding not only 
improves the colour, but renders working with the paint 
less difficult to manage ; the washing removes soluble 
sulphates and certain sulphur-compounds, which are liable 
to discolour some of the pigments (those containing lead 
or copper) with which the ultramarine may afterwards be 
associated in a picture. 

The hue of artificial ultramarine is commonly of a less 
pure quality than that of the natural pigment, verging 
somewhat towards a purple. But its range of hue is 
considerable, from a greenish-blue to a decided violet. 
The greenish-blue and blue varieties are not affected in 
hue by admixture with zinc white, but the varieties 
which incline towards violet become remarkably enfeebled 
in richness of colour by this admixture, such weakening 
being out of all proportion with the dilution of tint which 
would be expected to ensue from this addition of white. 
However, other white substances do not produce this 
curious result. 

Weak acetic acid, and a saturated cold solution of 
alum, which are without immediate action upon natural 
ultramarine, generally change the hue, and always ulti- 
mately decolourize the artificial product. Those kinds 
which have a somewhat violet tinge resist the destructive 
action of the above reagents longer than the pure blue 
and greenish-blue varieties. Neither sulphuretted hydro- 
gen, nor caustic lime or other alkaline substance, affects 
the colour of artificial ultramarine. 

Although the colour of ultramarine is certainly due to 
a substance containing sulphur, the precise chemical 
composition of this blue substance has not yet been 
determined. Some chemists are of opinion that it is a 
compound of aluminium, sodium, sulphur, and oxygen ; 



ARTIFICIAL ULTRAMARINE 231 

others regard it as a sulphide of aluminium. There is 
little doubt, however, that it contains sulphur in two 
conditions. Some curious derivatives of blue ultra- 
marine, of various colours, have been obtained, in which 
it is believed that the sodium of the original compound 
has been replaced by other metals ; such is the yellow 
'^silver-ultramarine,' prepared by keeping blue ultra- 
marine in a solution of silver nitrate. These bodies are, 
however, useless as pigments. The function of the silica 
in ultramarine is not known, although it forms from 
30 to 45 per cent, of the total weight of all the varieties, 
and although it has been found by experience that ultra- 
marines rich in silica resist the action of alum better 
than those which are poor in this constituent : these 
silicious ultramarines are sometimes sold under the name 
of ' Oriental Blue.' 

Artificial ultramarine, when properly prepared, is 
permanent both in water and oils. When thin washes 
on paper appear to lose strength as they dry, or soon 
afterwards, the change is due to the chemical action of 
the alum, or other aluminium compound, present in the 
size of the paper. If an ultramarine should discolour 
emerald green, chrome yellow, Naples yellow (true), or 
flake white, it probably contains free sulphur, or has 
been insufficiently washed. 

In order to test the purity of ultramarine, an easy plan, 
useful so far as it goes, is this : Boil a small quantity of 
the sample with distilled water in a wide test-tube for 
five minutes. Pour the liquid on to a wetted Swedish 
filter-paper fitted in a funnel. Divide the clear filtrate 
which runs through into 2 parts — to one add a few drops 
of basic acetate of lead ; to the other a few drops of 
barium chloride solution. No darkening should occur in 



232 ARTIFICIAL ULTRAMARINE 

the first case, nor any white cloudiness in the second. 
Besides the white adulterants, gypsum and heavy spar, 
both chessylite and Prussian blue have been found in 
artificial ultramarine. If chessylite be present, its 
presence may be detected by warming the sample with 
ammonia solution, when a blue solution will be obtained. 
Ultramarine containing Prussian blue acquires a brown 
hue when warmed with caustic soda solution, while it 
does not completely lose its blue colour when treated 
with dilute hydrochloric or sulphuric acid. 

When an acid (such as hydrochloric or oxalic) acts upon 
ultramarine, it disengages both sulphur and sulphuretted 
hydrogen ; a good deal of silica is also, in most cases, then 
separated in a gelatinous form. The sulphur separated 
as such may amount to as much as lo per cent, of the 
weight of the pigment taken, or it may be less than a half 
per cent. The sulphur disengaged as sulphuretted hydro- 
gen through the action of an acid varies between a half 
per cent, and 6 per cent. As these variations have no 
relation to the depth of colour in the several samples, it is 
evident that a great proportion of this sulphur does not 
form an essential part of the blue pigment itself. Other 
things being equal, it is well to select samples of ultramarine 
which contain as little as possible of sulphur in any 
state. 

The ultramarines known as * Guimet's ' and ' Heu- 
mann's ' are of fine quality. Large quantities of this 
pigment are manufactured in Germanyand France, smaller 
amounts in Belgium and England. The green, violet, 
lilac, purple and red ultramarines of commerce are per- 
manent pigments of some artistic value. They are or 
may be produced in the manufacture of the blue variety, 
the green being its precursor and the others being formed 



ARTIFICIAL ULTRAMARINE 233 

by further heating or treatment of the blue kind. The 
final product is a greyish-white body. 

There are two easily applied tests which, taken together, 
enable one to estimate the relative values of a set of 
samples of ultramarine in powder. These tests have dis- 
tinct objects in view. In one, resistance to alteration is 
determined — in the other, the colouring power. The 
quantity operated on is only 5 centigrams, so the best 
plan is to begin by weighing out, with the aid of a sensi- 
tive balance, two portions of -05 gram a-piece from each 
sample. One of each of these portions is thoroughly 
mixed, by means of an ivory spatula, on highly glazed 
white paper, with 2 grams of pure kaolin : the tints of 
the several kinds are then compared. For the other test 
we require a number of small precipitating glasses or 
large test-tubes, and a supply of a saturated solution of 
potash alum in distilled water. The five centigrams of 
each sample of ultramarine are put into the duly labelled 
glasses and a measured quantity (say 50 cubic centi- 
metres) of the alum solution is poured on with constant 
stirring. The change or loss of colour is duly noted at 
intervals of time, some samples opposing a resistance of 
days to the destructive influence of the alum, while others 
are injured by a contact of a few hours, or, in some 
extreme cases, of a few minutes. It is scarcely necessary 
to add that the contents of each test-glass should be 
thoroughly stirred at regular intervals. To avoid this 
necessity, and at the same time to improve the accuracy 
of the results, a slight modification of the method may be 
introduced. Ten grams of the purest agar-agar are dis- 
solved by the aid of heat in a litre of the alum solution. 
Just before this liquid has become a jelly by cooling, a 
measured portion is poured upon the necessary quantity 



234 COBALT BLUE 

of ultramarine : the mixture after thorough agitation is 
allowed to set, so that the pigment remains suspended 
throughout the mass ; any changes of colour can be 
easily recognised. 

Cobalt : Cobalt Blue — Bleu de Thenard — Kohalthlau. 

Excluding smalt, which owes its colour to a cobalt 
silicate, there are at least three pigments which go under 
the name of ' cobalt ' or ' cobalt blue.' The best known 
of these is a combination of alumina and cobalt oxide ; 
then comes Leithner's or Thenard's blue, a cobalt phos- 
phate on an aluminous base ; lastly, there is an aluminous 
cobalt arseniate very much like the phosphate. 

The original and simplest form of cobalt blue, or 
Wenzel's blue, may be made by calcining strongly an 
intimate mixture of aluminium hydrate and cobalt oxide. 
A better way consists in moistening freshly-precipitated 
aluminium hydrate with a solution of cobalt nitrate, dry- 
ing and then strongly igniting the mass. It may likewise 
be prepared by precipitating a solution of sodium alumi- 
nate by means of cobalt chloride solution. Thenard's blue 
may be prepared by mixing about 8 parts of aluminium 
hydrate with i part of cobalt phosphate, both in the moist 
condition, then drying and strongly calcining the mixture ; 
cobalt arseniate may replace the phosphate. Another 
variety of Thenard's blue is obtained by adding sodium 
phosphate solution to a solution of alum containing a little 
cobalt sulphate. In all the above methods, the complete 
freedom from iron and nickel of the materials used is 
essential to the purity and beauty of the blue pigment 
formed. 

The cobalt blues work well in all media. They are un- 
affected by light, moisture, and oxygen. The best samples 



CCERULEUM 235 

of them are practically permanent even in impure air, but 
ammonium sulphide tends to discolour them. If they 
appear changed in hue in any oil-paintings, the yellowing 
of the admixed or overlying oil or varnish must be regarded 
as the cause. Cobalt blues may be used in fresco-painting ; 
they are unaffected by commixture with other pigments. 
Cobalt blues do not lose their colour when boiled with 
alum solution, nor when treated with moderately strong 
acids. 

Cobalt blue as an oil-colour is usually ground with about 
three-fourths its weight of linseed or poppy oil. 

Cobalt blue examined optically is found to reflect much 
green and violet Hght as well as blue. Viewed by candle 
or gas light it acquires a very marked purplish hue. 
Burton's cobalt, originally prepared for the use of potters, 
is of fine quality and of more than usual stability. 

The introduction of cobalt blue to the palette of the 
artist may be said to have created a revolution in the 
style of painting, especially obvious in water-colour land- 
scapes. 

CcERULEUM : Cenilium — Cerulean Blue — Coelinhlau — 
Bleu Celeste. 

When oxide of tin is moistened with cobalt nitrate solu- 
tion and strongly heated, a greenish-blue mass is obtained, 
which, after powdering and washing, constitutes one of 
the varieties of the pigment known as coeruleum. There 
are other ways of preparing this substance. One of these 
consists in precipitating potassium stannate with cobalt 
chloride, collecting and washing the precipitate, and then 
mixing it with some pure silica and heating it. A good 
specimen of cceruleum contained in 100 parts : 49-7 tin 
binoxide, 18*6 cobalt oxide, and 317 silica. Some samples 



236 PRUSSIAN BLUE 

contain calcium sulphate, or lead sulphate, in place of the 
silica ; they are of inferior quality. 

Coeruleum is a permanent pigment of a rather greenish- 
blue colour, without any tendency to the violet cast, so 
noticeable with other cobalt blues (page 235), when viewed 
by gas or candle light. It suffers little, if any, change by 
exposure to light or impure air, or by commixture with 
other pigments. It is a sub-opaque, rather earthy pig- 
ment, with a moderate tingeing power. Although some 
painters find it useful, coeruleum may be imitated so 
nearly by a mixture of ultramarine, viridian, and white 
that its presence on the palette can easily be dispensed 
with. 

Prussian Blue : Timibuirs Blue — Antwerp Blue — Berlin 
Blue — Pnissiate of Iron — Chinese Blue — Saxon Blue — 
Bleu de Berlin — Pariser-blau. 

Although the chemical constitution of this pigment can 
hardly be said to have been absolutely ascertained, yet it 
is generally believed that there are at least three different 
though closely allied chemical compounds included under 
the above names, not to mention those varieties of this 
pigment which contain added or extraneous substances, 
such as alumina, plaster-of- Paris, or zinc-white. The 
three typical and distinct compounds are : 

I. Soluble Prussian Blue. — This is made by pouring a 
solution of ferric chloride or ferric nitrate into an excess 
of potassium ferrocyanide solution (yellow prussiate of 
potash), or by pouring ferrous sulphate solution into 
excess of potassium ferricyanide solution. The blue 
precipitate formed is washed with distilled water until 
the wash-water begins to acquire a blue tint. The com- 
position of the pigment thus prepared is, when dry, 



PRUSSIAN BLUE 237 

represented by the formula K2Fe2(CN)j2Fe2. It con- 
tains potassium, and is, in reality, a double ferrocyanide 
— a ' potassio-ferric ferrocyanide.' It is less stable than 
either of the other kinds of Prussian blue, while its solu- 
bility in water causes it to stain the paper on which it is 
spread in water-colour painting. It should invariably be 
rejected by artists, although it must be owned that it 
works very smoothly both in water and in oil. It may 
always be distinguished from the superior kinds of 
Prussian blue by very simple tests. One of these con- 
sists in roasting a small portion of the dry powdered pig- 
ment in a porcelain basin or iron tray, allowing the 
brown residue to cool, and then throwing it into a little 
pure water. Then place the mixture on a wetted filter 
contained in a funnel, and see whether the clear filtrate 
is alkaline by dipping a piece of yellow turmeric paper 
into it ; if the yellow tint of this paper is reddened, then 
the Prussian blue belongs to this section. Another test 
is applied by simply washing some of the powdered blue 
with warm distilled water on a Swedish filter — the filtrate 
becomes blue. 

II. Insoluble Pntssian Blue may be prepared by boiling 
No. I. (the soluble kind) with a solution of ferric chloride, 
by mixing solutions of ferrocyanic acid and ferric chloride, 
by pouring potassium ferrocyanide solution into an excess 
of a solution of ferric chloride, or of ferric nitrate, and 
heating the mixture for some time, or by precipitating a 
watery solution of Blue No. I. with an excess of either 
of the above-named iron salts. It may also be obtained 
by oxidizing Turnbull's blue (No. III.) with chlorine 
water or nitric acid. The chemical composition of this 
pigment is very complex, the simplest empirical formula 
for it being Fe7(CN)ig: it will be seen that it contains no 



238 TURN BULL'S BLUE 

potassium. It always contains some combined water, 
which cannot be driven off by heat without decomposition 
of the salt. This blue is more permanent than No. I. 

III. Tuvnhuirs Blue. — The chief constituent of the 
original Turnbull's blue (more properly, Gmelin's blue) 
closely resembles ordinary soluble Prussian blue, and, 
like it, contains potassium. But the potassium may be 
removed from it by stannous chloride solution, a sub- 
stance being produced having the empirical formula 
Fe5(CN)i2, but containing some water. Or the same 
body may be made by precipitating a solution of ferri- 
cyanic acid with a solution of ferrous sulphate or ferrous 
chloride. This blue is of good colour, but is more diffi- 
cult to obtain pure than No. II., the other insoluble 
Prussian blue. Exposed to light, all the forms of Turn- 
bull's blue, pure and impure, have a more decided ten- 
dency to become greenish or to fade than No. II. 

The ordinary commercial Prussian blue is a mixture, 
in varying proportions, of the three blues above de- 
scribed. It is made by adding green vitriol (ferrous 
sulphate) solution to a solution of yellow prussiate of 
potash (potassium ferrocyanide). The precipitate formed 
(which varies in colour from a light to a deep blue, 
according to the amount of ferric salt present in the 
green vitriol) is then oxidized by means of dilute nitric 
acid or of a solution of bleaching powder. After having 
been washed, the substance is treated with hydrochloric 
acid, and is then again washed with water. 

All the above blues are of a very deep blue colour 
in powder or in the lump, but when pressed or rubbed 
they all show a coppery lustre. The only one fit for 
artists' use is the insoluble variety (No. II.), the others 
being less stable or having other defects. The insoluble 



PRUSSIAN BLUE 239 

form is, moreover, the only one which yields, when 
roasted, a perfectly satisfactory ' Prussian brown.' 

Prussian blue is a transparent colour of great force and 
richness, and works well in oil as well as in water. In 
thin washes or layers it has a slightly greenish hue. Its 
colour is changed by lime and by the weakest alkalies, so 
that it cannot be employed in fresco or on newly-plastered 
walls. Long-continued exposure to strong light weakens 
and alters the colour of Prussian blue, but the insoluble 
varieties are less affected than the soluble. When this 
fading of the pigment in water-colour washes has taken 
place, a brief sojourn in darkness generally suffices to 
restore the hue almost to its original depth and quality. 
This strange phenomenon, which awaits explanation, has 
been long familiar to artists' colourmen. The influence 
of moisture in determining the fading of Prussian blue 
under solar exposure is seen in three comparative trials 
with water-colour washes on paper. In a sealed tube 
with ordinary air the intensity was reduced from 10° to 
1°, and the colour became sea-green in thirteen months ; 
after four years a part of the same wash retained its full 
depth when the slip was exposed in air kept dry ; another 
portion was reduced to 8-5° by four years' exposure in 
an ordinary frame. A sample of Prussian blue (as 
ordinarily made) in oil, after five years' exposure, had 
become somewhat greenish, with a loss of about one- 
tenth of its depth. These changes were more obvious in 
the pure transparent pigment than in its tint with flake- 
white. A second specimen, from another maker, similarly 
exposed, was rather less affected, both as to loss of colour 
and as to change of hue. 

Prussian blue was discovered in 1704 by a colour- 
maker of Berlin, Diesbach by name. When, as is some- 



240 CYAN IN E 

times the case, this pigment is found in water-colour 
paintings of the seventeenth century, it is scarcely neces- 
sary to state that its presence betrays the brush of the 
restorer or the forger. 

Antwerp blue is a sort of Prussian blue lake, the pig- 
ment consisting of a colourless base dyed with Prussian 
blue. According to one method of preparation, a solution 
of I part of green vitriol and 2 parts of zinc sulphate in 
40 parts of water is precipitated by adding to it a solution 
of 4 parts of potassium ferrocyanide in 40 parts of water. 
The blue colour of the precipitate deepens as it is washed. 
Alumina is sometimes used as the base upon which the 
blue pigment is thrown. Antwerp blue is less transparent 
and less intense in colour than Prussian blue ; it has 
about the same degree of stability. 

Cyanine : Leitch's Blue. 

A mixture of Prussian blue and cobalt blue has been 
sold under the name of cyanine. It would seem from 
some recent experiments made with this mixed pigment 
that it is fairly permanent, even in water-colour painting. 
It is, of course, not adapted for use in fresco, as the Prus- 
sian blue in it at once yields rust through the action of the 
lime of the intonaco. Mixed pigments cannot, however, 
be recommended, as it is in nearly all cases better for the 
artist himself to associate together those paints which he 
wishes to mingle. This plan gives him the opportunity 
of ascertaining the purity and quality of the several com- 
ponents of his mixtures. In the case of cyanine, it 
appears that the more permanent constituent, the cobalt, 
partially protects the Prussian blue from change — a result 
which is still better seen v/hen a separate wash of cobalt 
is laid over a wash of Prussian blue. In this case the 



INDIGO 241 

light which has penetrated through the cobalt particles 
would seem to have been deprived of those rays which 
effect the decomposition of the Prussian blue beneath. 
Such a phenomenon is not unusual, and has been ob- 
served in the case of several pairs of pigments having 
very closely-allied hues. 

Indigo. 

Indigo has been used either as a pigment or a dye from 
very early times in India and in Egypt. It is referred to 
under the name of indicum by Pliny; later on the Byzantine 
writers called it azovmni Romanum. ' Indigo bagadel ' — 
that is, indigo of Bagdad — is named as early as 1228 in 
the Marseilles tariffs ; in the early English accounts rela- 
ting to painting works (1274) it is called ' indebas.' In 
the fourteenth century it was designated as ' ind,' ' inde,' 
and ' ynde.* ' Endego ' and ' indico ' were used in the 
sixteenth and seventeenth centuries. It was first largely 
imported from India into Europe in the seventeenth cen- 
tury by the Dutch. 

A large number of different plants yield true indigo. 
This pigment was once obtained in considerable quantity 
from a crucifer, I sat is tinctoria, the dyers' weed or woad, 
the ' pastel ' of the French ; but the chief source is now 
Indigofera tinctovia, a leguminous shrub, probably of 
Indian, or at least Asiatic, origin. 

Indigo (CjgHjoNgOg) does not exist ready-formed in the 
plants which yield it, but occurs in the form of a colourless 
compound, or glucoside, which, by combining with water, 
splits up into a sugar and indigo. It is prepared from the 
freshly-cut plants, or from the dried foliage, by maceration 
in water and fermentation, followed by boiling (sometimes 
lime-water is first added) ; the dark precipitate which forms 

16 



242 



INDIGO 



is thrown on to cloth-strainers, and finally pressed and 
dried. The mineral impurities which commercial indigo 
contains are derived partly from the plant itself, partly 
from the water used in preparing it, and partly from the 
lime-water above mentioned ; moreover, it is sometimes 
adulterated. Indigo is easily oxidized by a very large 
number of substances rich in oxygen, yielding a yellow 
product called isatine ; it is converted into a colourless 
body (CjgHjgNgOg) by many reducing agents. 

Indeed, several of the processes of purifying indigo 
depend upon the reduction of the blue colouring sub- 
stance, or ' indigotin,' into ' white indigo,' and the subse- 
quent precipitation of the blue matter by exposure to the 
oxygen of the air. Green vitriol is the commonest reducing 
agent, and is used in association with lime. The purified 
indigo prepared by this process, though of fair colour, does 
not, however, work so well as a paint as the best Bengal 
indigo treated successively with acid, alkali, acid, and 
alcohol. Indigotin, if quite pure, has a somewhat purplish 
cast in thick water-colour washes ; this hue is observable 
with this substance whether obtained by sublimation or 
by Fritzche's process with grape-sugar, caustic soda, and 
alcohol. 

The impurities in commercial indigo constitute from 
20 up to 70 or 80 per cent, of its total weight — the 
average is about 50. They consist mainly of mineral 
matter, indigo red, indigo brown, and nitrogenous com- 
pounds. Much of the mineral matter may be removed 
by digestion in hydrochloric acid, followed by treatment 
with boiling water. Sodium hydrate solution dissolves 
the indigo brown, while strong alcohol takes away the 
indigo red, which amounts to nearly 4 parts in 100 of 
the original indigo. After treatment with these three 



INDIGO 243 

solvents, the residual purified indigo is of an intense and 
very beautiful hue. Java indigo is generally of very 
good quality, that from Bengal comes next, and then 
the indigo from Oudh, Kurpah, and Madras. Japanese 
indigo is generally poor. 

Indigo frequently receives no purifying treatment 
previous to its being ground into a fine powder suitable 
for admixture with oil or with gum and the other media 
of water-colours. The necessity of choosing the purest 
and finest samples of the commercial dye-stuff is of 
course evident, but it is better in every case to adopt the 
processes of purification named in the preceding para- 
graph. No sample of purified indigo should leave, after 
being burnt, more than 3 per cent, of ash. 

This rich and transparent blue is, unfortunately, 
gradually oxidized and browned when exposed to light. 
In thin washes of water colour it disappears rapidly in 
the sun's rays, much more slowly when submitted to 
diffused daylight. The following figures approximately 
represent the reduction in force of a sample of indigo as 
a moist water-colour when exposed to sunlight : 

Original intensity ... ... ... 10 

After two years ... ... ... i 

After ten years ... ... ... o 

Other trials with other samples gave in some cases less 
unfavourable results. 

Indigo in cake is sometimes less affected by sunlight 
than the moist preparations. As an oil-colour, indigo 
loses from one-third to one-half of its intensity when 
exposed to sunlight for five years, its hue being at the 
same time altered, in different specimens, either to a 
greyish or a greenish blue ; the change is more con- 



244 INDIGO 

spicuous when the indigo has been mixed in tint with 
flake or other white. Locked up in copal or amber 
varnish it is more slowly changed. The fading is due to 
oxidation. 

Indigo may be replaced advantageously by ultramarine 
mixed with a trace of viridian, or by a good Prussian 
blue, either being associated with a little ivory-black. 

Several pigments, such as aureolin, true Naples yellow, 
and all the chromates, have a very marked effect upon 
indigo. 

In order to ascertain whether the fading of indigo as a 
water-colour, on exposure to sunshine, was increased by 
the presence of alum in the paper, a series of comparative 
experiments were made. A pale tint of indigo was 
spread upon (i) paper free from alum; (2) paper washed 
with alum solution ; (3) paper containing a trace of 
alum ; (4) paper which had been washed with weak 
ammonia-water after having received an alum-size. 
After six months' (April to September inclusive) exposure 
to sunlight, all the four specimens showed complete 
extinction of the blue pigment, the disappearance of the 
colour from No. 2 having, however, been a trifle more 
rapid than in the other cases. Honey and glycerin, 
owing to their hygroscopic character, appear to hasten 
the fading, so does water-vapour; for a dried sHp of 
indigo-washed paper sealed up in a glass tube loses its 
colour less quickly than one in its ordinary moist con- 
dition, when both are exposed side by side to sunshine. 
A tightly-framed water-colour drawing presents, of course, 
a close analogy to the second or more unfavourable set of 
conditions. When a medium tint of indigo on paper was 
exposed for four years to sunlight in a tube containing air 
kept dry by a water-absorbing agent, its original depth of 



INDIGO 245 

colour was perfectly preserved. An identical experiment 
in an ordinary glazed frame resulted in a reduction of 
tone from 10° to 1°, while the residual hue was a greenish 
grey. 

The effect, if any, of the several iron reds, such as light 
red, Venetian red, and Indian red, in accelerating the 
fading of indigo in sunshine has been tested in many ways. 
Provided the three red pigments above-named be free 
from soluble salts, and especially from sulphates, they are 
equally innocuous ; the indigo disappears with or without 
them at the same rate. In one instance only a wash of 
Venetian red with indigo lost its indigo completely three 
weeks before the destruction of the blue in the parallel 
experiments was complete, which was the case in six 
months. It is impossible to assert that this result was 
not due to a smaller amount of indigo having been pres- 
ent in this particular case, but I believe it to have been 
due to this sample of Venetian red having been an imita- 
tive one prepared from colcothar. 

In comparing under the same conditions the relative 
stability, when exposed to light, of different indigoes, it 
appears that ' Bengal refined ' is superior to the best ' raw 
Bengal,' and even to the indigotins obtained by the green 
vitriol and glucose processes. 

The superiority, when exposed to light, of refined indigo 
— that is, of indigo which has been purified by the treat- 
ment with acid and the other solvents already named — 
although observed in recent experiments, seems to have 
been ascertained in the time of De Mayerne. One of the 
authorities (Elias Feltz, of Constance) quoted by De 
Mayerne affirms that this pigment may be rendered safe 
by steeping it in vinegar and exposing it to the sun for 
several days ; the vinegar is then to be poured off, and 



246 INDIGO 

the paste when dry ground in oil. Another plan recom- 
mended (in a note, dated 1642) by Feltz consists in grind- 
ing the indigo with a little calcined alum ; this plan is, 
however, objectionable for several reasons. The treatment 
of the indigo with the solvents previously named, which 
are adapted to remove its natural impurities, is the only 
legitimate plan. It is scarcely necessary to add that there 
is abundant evidence to prove that in De Mayerne's day 
indigo was generally regarded as an unstable colour. 
Under all circumstances no indigo should be employed in 
painting unless it be completely free from acids. 

Although it is not possible to ascertain the exact rich- 
ness in indigotin of commercial indigoes by any tests save 
those in use by professional chemists, yet it is easy to 
learn a good deal about any particular sample by means 
of a few simple experiments. A good sample should 
appear homogeneous, and should float on water. Dried 
at 100° C, it should not lose more than 6 parts per 100 of 
moisture. When rubbed with a hard smooth substance 
it should show a coppery lustre. One hundred grains 
when burnt should not leave more than 10 grains of grey 
ash. It should dissolve perfectly in four times its weight 
of fuming sulphuric acid. Starch, gypsum, clay, chalk, 
steatite, and Prussian blue are amongst the adulterants of 
indigo. 

Indigo dissolved in four times its weight of fuming oil 
of vitriol (kept cool) forms a liquid from which, after 
slight dilution and filtration through asbestos cloth, potas- 
sium carbonate precipitates a fine blue compound, which 
has been used in water-colour painting under the name of 
indigo carmine. It is not a safe pigment. 

The artificial or synthetic indigo, although characterized 
by freedom from impurities, both organic and inorganic. 



INDIGO 247 

does not offer any advantages over the natural product, 
if properly purified, when employed as a paint in water- 
colour or oil. It may be added that those derivatives of 
indigotin, in which some of the hydrogen atoms have been 
substituted by bromine or chlorine, are no more perma- 
nent than the original dyestuff. This is the case with 
that form of dibrom-indigotin (the punicin of the late 
H. E. Schunck), which occurs naturally in, or rather was 
obtained from, certain marine molluscs [Purpura lapillus 
and Murex brandaris), and which has been known for 
many centuries as Tyrian Purple. The very minute yield 
of the natural pigment would have made its general use 
impracticable, but now that the identical substance can 
be freely made from indigo, it is found that its lack of 
permanence should exclude it from the 'selected' palette 
of the artist of to-day. 

In examining old water-colour drawings, it will often be 
found that the parts protected by the mount or frame show 
the indigo used in compounding the greys of clouds and 
the greens of vegetation perfectly intact, while it has com- 
pletely left the exposed parts. In many cases where indigo 
is supposed to have withstood long exposure to light, it 
will be found that the blue used has been Prussian blue, 
modified by admixture with other pigments. But in many 
old pictures and drawings it will be found that the un- 
natural bluish hue of the foliage represented is due to the 
complete loss of rapidly evanescent yellows, rather than to 
the entire stability of the indigo with which the greens have 
been compounded. Nor must it be forgotten that indigo 
was not the only blue in such mixed greens, blue carbonate 
of copper and even lapis-lazuli having been extensively 
employed at that time. The latter pigment is perfectly 
permanent except in the presence of acids and alum. 



248 SMALT 

Smalt : Royal Blue — Dumonfs Blue — Zaffre — Bleu de 
Smalte — Smalte — Zaffev. 

Glass and vitreous mixtures containing cobalt, and of 
a rich blue colour, have been known for ages, although 
copper, not cobalt, was the colouring principle of most of 
the antique materials of this class. The smalt now made 
is a very deep-blue glass (appearing black in the lump), 
consisting essentially of cobalt and potassium silicate. It 
generally contains, in 100 parts, silica, 65 to 71 ; potash, 
16 to 21 ; and cobalt oxide, 6 to 7 parts : a little alumina 
is always present. In the inferior varieties the oxides of 
iron and nickel always occur. 

In order to prepare a pigment from the dark cobalt glass, 
it is fused, and then poured into cold water. After the 
disintegration thus effected, the glass is ground into a 
moderately fine powder, and submitted to the process 
called elutriation, or washing-over. The finest particles, 
which take longest to settle from the wash-waters, are 
the palest in colour ; the larger particles, though of richer 
hue, are very difficult to use as a paint. 

Smalt is rarely employed now as an artists' pigment, 
cobalt blue and artificial ultramarine having been very 
advantageously substituted for it. For not only is it a 
difficult pigment with which to work, in both water and 
oil, but it is gradually altered by moisture and by the 
carbonic acid of the air, becoming paler and greyer ; more- 
over, the finer the state of division in which it exists, the 
more rapid is the change. It will be found that even 
spring or distilled water is competent to start the decom- 
position of smalt. For if a little of this pigment be placed 
on a piece of yellow turmeric-paper, and moistened with 
clean water, there will soon be formed a red stain beneath 



CHESSYLITE 249 

the smalt — proof of the Hberation of some of the alkaUne 
constituent (potash) of this blue glass. 

Chessylite : Bhce Vevditev — Bice — Mountain Blue — 
A ziivite — Cendves Bleues — Bevghlau. 

This copper mineral differs from malachite in containing 
less hydrate, or more carbonate of the metal, its composi- 
tion being represented by the formula aCuCOg, CuHgOg. 
Its best-known locality is Chessy, near Lyon, in France, 
but very fine specimens are found at Wallaroo and 
Burra-Burra, in South Australia, and in the district of 
Perm, Siberia. 

This blue pigment has been prepared artificially, but 
the natural substance is far less liable to change on 
exposure to impure air. The introduction of cobalt blue, 
and more particularly of artificial ultramarine, has 
practically caused the disuse of blue verditer, or rather 
of chessylite ( = azurite), this beautiful native blue pig- 
ment, which, when used in illuminated manuscripts, as 
was largely the case between the thirteenth and six- 
teenth centuries, has kept its hue unimpaired to the 
present day. 

Under the name of Bleu Lumi^re a beautiful turquoise- 
coloured paint was introduced to artists. It consists 
mainly of an artificial copper hydrate along with some car- 
bonate. It becomes greenish by exposure to sunlight or 
a very moderate degree of heat. Like all similar artificial 
compounds of copper it proves to be untrustworthy. 

Many old pictures, especially those in tempera, afford 
evidence of the blue hydrato-carbonates of copper having 
become green. With the extensive range of more per- 
manent blues at the command of the modern artist, 
there is no need to retain this pigment on the palette. 



250 BLUE PIGMENTS 



Egyptian Blue. 



A beautiful and permanent blue pigment, generally 
known as Egyptian blue, has been studied by many 
chemists. It is found on objects of Egyptian origin 
from the time of the fourth Dynasty onwards, and 
was in use during the time of the Roman Empire. 
Specimens have been found in Pompeii and other Roman 
sites ; also in Britain, at Wroxeter, in Syria, and in 
Crete. Our knowledge of this pigment has become more 
exact in consequence of the researches* of Professor A. 
P. Laurie, who has re-determined its chemical composi- 
tion as well as its physical properties, and has, moreover, 
ascertained the precise conditions under which it is pro- 
duced. In one of Professor Laurie's trials he took i8o 
parts of fine sand, 48 copper carbonate, 36 calcium car- 
bonate, and 20 parts of ' fusion mixture.' A few grams 
were submitted to definite temperatures in an electric 
furnace for some hours, the mass being cooled, re-ground, 
and re-heated. Finally it was found that the optimum 
temperature for the production of the crystalline blue 
was somewhere about 830° — 850° C. The crystals, 
which are transparent and dichroic, and have a density of 
3, consist of a double silicate of calcium and copper, 
represented by the formula CuO,CaO,4Si02, but gener- 
ally containing about 2 per cent, of potash and soda, as 
substituents for a part of the copper and calcium oxides ; 
the actual percentage of copper oxide present in the 
pure blue is therefore usually somewhat lower than the 
theoretical. It should be added that the interest at- 
tached to the subject of Egyptian blue is rather academic 

* Proceedings of the Royal Society, A. (1914), vol. 89, pp. 418-429. 



MANGANESE VIOLET 251 

than practical, for this pigment is not now made except 
on a small laboratory scale, and has not found for many- 
centuries a place on the palette of the artist. 

Manganese Violet : Mineral Violet — Permanent Violet — 
N limber gevviolett . 

This pigment is rarely met with on the palette of the 
artist ; it is, however, quite permanent and has a truer 
violet hue than cobalt violet, which is redder as well as 
brighter. Its preparation is somewhat tedious. It is 
made by means of manganous chloride and phosphoric 
acid, solutions of these compounds being mixed together, 
evaporated to dryness, and then the residual mass fused. 
The fused mass is broken up and boiled with a solution 
of ammonium carbonate. The turbid liquor is allowed 
to settle, and then the clear portion is decanted or filtered 
off and evaporated to dryness, and the residue fused. By 
grinding the fused mass and boiling it with water a fine 
precipitate of ' manganese violet ' separates : it is re- 
moved by filtration and thoroughly washed and dried. 
It appears to be essentially manganous metaphosphate, 
although by no means pure. 

Two other violet or purple pigments of a permanent 
character have been already described. One of these is 
violet cobalt (page 211), the other violet ultramarine 
(page 232). 



CHAPTER XVIII 

BROWN PIGMENTS 

Raw Umber : Levant Umber — Terre d'Ombre — Umbraun — 
Umbra — Terra Ombra. 

This earth is found in several localities ; the best variety 
has come for some time past from Cyprus. A consider- 
able number of Cypriote specimens, of several nuances, 
some excellent, were shown in the Colonial and Indian 
Exhibition of 1886. It differs chemically from the yellow 
and brown ochres in several particulars, notably in the 
presence of a considerable quantity of one of the higher 
oxides of manganese (Mn^O^, or MnOg), and in the small 
proportion of water which it contains. Samples from 
English localities are poor in iron ; one Derbyshire 
specimen gave Mr. G. H. Hurst no less than 30 per 
cent, of barium sulphate. An analysis of my own, made 
with a choice sample from Cyprus, showed the following 
percentages : 



Water, lost at 100° C. - 4*8 
Water, lost at a red heat*- 8*8 
Iron oxide (FcgOa) ' - 48 '5 
Manganese dioxide (Mn02) i9"o 
Lime - - - - - i"4 



Magnesia - - - - 0*5 

Alumina - - - - 2-1 

Phosphorus pentoxide - 0*9 

Silica 13-7 

Carbon dioxide, etc. - - 0*3 



This sample had the peculiar greenish hue so much 

* Includes a little organic or bituminous matter. 
252 



RAW UMBER 253 

prized by artists. It should be stated that a part of the 
manganese probably existed as MngO^. 

Before being used as a paint, this brown mineral is 
finely ground, washed with water, and then dried at 
100° C, or at a slightly higher temperature. When, by 
a stronger heat, the whole of its water has been expelled, 
the umber acquires a reddish hue, and is then the pig- 
ment known as burnt umber. This change of colour is 
due to the passage of the brown ferric hydrate into the 
red ferric oxide, and to an increase in the proportion of 
the red-brown manganese oxide present. 

Raw umber in powder, after having been purified, soon 
acquires a very slight reddish hue on exposure to light 
and air ; it is a good plan to place the undried, finely- 
ground mineral on trays in the sunshine before completing 
its desiccation and mixing it with oil or other medium. 

Raw umber is permanent when used with each or any 
of the painting media : the slight yellowish or dull aspect 
which it acquires in oil may be traced to the augmented 
translucency of the paint, and to the yellowing of the 
associated oil. Umber is without action on other pig- 
ments. A very few samples of umber, used as a water- 
colour, have been observed to fade slightly after from 
five to ten years' exposure to sunlight. But this 
deterioration is due to the presence of traces of brown 
peaty acids, or ' humus ' substances, which occasionally 
occur in the umbers from certain localities. 

Raw umber possesses a semi-opaque, citrine-brown 
colour ; it works and dries well in oil. Associated with 
transparent blues, it yields soft, quiet green hues ; it is 
invaluable both in figure and landscape painting. As a 
priming or first painting-ground, it is apt, like most dark 
pigments, to become more conspicuous in time, owing 



254 RA W SIENNA 

chiefly to the translucency which the superimposed 
painting gradually acquires. 

Raw umber is not subject to aduheration, but a ferru- 
ginous brown coal has been occasionally substituted for 
the true mineral. The great variation in quality shown 
by the umbers of commerce is due, in great part, to the 
difficulty of securing, even from the same mine, con- 
tinuous supplies of the same excellence. 

Burnt Umber. 

It has before been pointed out that raw umber, from 
which burnt umber is prepared by calcination, is not an 
ordinary ochre, but owes its colour in great measure to 
the presence of a considerable amount of some compound 
of manganese. The exact constitution of raw umber is 
not, however, known, although the slight change in hue 
which occurs when it is roasted negatives the idea that 
it contains any considerable proportion of the ordinary 
ferric hydrates. If these were present in notable propor- 
tions, roasting would certainly redden raw umber much 
more than is actually the case. 

Burnt umber differs in quality and hue from the raw 
earth mainly in being more translucent, and of a warmer 
brown. Although some Continental authorities affirm 
that this pigment darkens and becomes purplish in course 
of time, I cannot regard it as otherwise than perfectly 
permanent, and as exerting no action on stable pigments. 

Raw Sienna : Terre de Sienne — Terra di Siena — Rohe 
Sienna. 

This earth, which is found chiefly in Tuscany and the 
Hartz, is a particularly rich variety of yellow ochre, and 
contains a large proportion of a ferric hydrate. The late 



RA W SIENNA 255 

G. H. Hurst (' Chem. News,' vol. lix., p. 172) gave three 
analyses of raw sienna. In these the range in the 
percentages of the more important constituents is as 
follows : 

Hygroscopic water ... ... 8-2 to 17-5 

Combined water "^ ... ... 9*0 „ i2'4 

Manganese dioxide ... ... o-6 „ 1-5 

Iron oxide (FegOg) ... ... 45"8 „ 597 

Silica 5'o „ 17*4 

Raw sienna is prepared for use by crushing, sifting to 
remove sand, grinding and washing in the same way as 
in the case of yellow ochre. It should be noted that 
when lumps of fresh raw sienna are first broken and 
exposed to the air, their surfaces acquire a slight olive- 
green nuance. In order to avoid any disadvantage which 
might arise from such an alteration taking place subse- 
quently, it is a good plan to expose the crushed earth to 
the air and light previous to its final preparation as a 
pigment. Before grinding it in oil, it should be cautiously 
dried at 60° C. to remove the greater part of the accidental 
or hygroscopic moisture. 

Raw sienna in thick washes is somewhat deeper in 
tint and of a warmer and browner hue than yellow ochre. 
Owing to a trace of organic or peaty matter which it 
contains, raw sienna is liable to become rather less brown 
and more yellow by long-continued exposure to strong 
light. It is generally without action on other pigments, 
and is available for water-colour, oil, and tempera paint- 
ing ; it sometimes fails in fresco. A given weight of raw 
sienna requires a larger proportion of oil than any other 
pigment ; the finished oil-paint contains only 30 per cent, 
of pigment. 

* Includes traces of organic matter. 



256 CALEDONIAN BROWN 

Raw sienna is not subject to adulteration, but it is well 
to be certain that the pigment has been well washed. 

Burnt Sienna. 

The roasting or calcination of raw sienna produces a 
very great change in its hue as well as in the depth of its 
colour. The ferric hydrate of the raw earth becomes 
wholly converted into ferric oxide, this change being 
accompanied by a great increase in the translucency and 
depth of the colour. 

When small fragments (or the coarse powder) of raw 
sienna are calcined, it will be noticed that the change of 
hue which occurs is not quite uniform, some points being 
of a brighter and redder brown than others. A very fine 
powder, thoroughly stirred during roasting, shows this 
peculiarity in a much less marked degree. 

Burnt sienna possesses a very beautiful, warm, reddish- 
brown hue, which cannot be exactly imitated in trans- 
lucency and depth by mixtures of other pigments. It is 
permanent, without action on other pigments, and not 
liable to adulteration. It is available for use in every 
method of painting. Some fine and permanent foliage- 
greens may be made by associating viridian with burnt 
sienna. 

Caledonian Brown. 

This brown, although a natural earth, presents very 
much the appearance of burnt sienna. It contains a 
small quantity of combined moisture. It consists mainly 
of the brown hydrates and oxides of manganese and iron. 
When calcined it loses its ruddy hue and becomes almost 
black — a black with a slight brownish hue. 

Caledonian brown, whether raw or burnt, is a per- 



VANDYKE BROWN 257 

manent and innocuous pigment, which is well adapted 
for oil and tempera painting. It is said that the original 
source of this pigment is exhausted, and that an imita- 
tive mixture of burnt sienna and bituminous Vandyke 
brown is sold in lieu of Caledonian brown. 



Vandyke Brown. 

Three brown pigments pass in commerce under the 
name of Vandyke brown. The first is made by calcining 
certain very ferruginous earths or brown ochres ; the 
second is nothing more than a dark-brown variety of 
colcothar ; the third is a kind of brown earth containing, 
along with some iron oxide and hydrate, a good deal of 
organic substance in the form of humus or bituminous 
matter. The first and second kinds are permanent and 
innocuous, but the third kind will not resist the pro- 
longed action of light, becoming paler and redder in the 
course of time. The discrepancies in the published state- 
ments as to the permanence of this pigment are thus 
readily explained ; it is to be regretted that most of the 
samples of Vandyke brown now met with in England 
belong to the third kind, and therefore fade quickly in 
water-colour, more slowly in oil. This sort may be 
recognised by the dark sublimate which it yields when 
its powder is heated in a test-tube, as well as by the 
change in colour and great loss of weight which it then 
shows. We shall designate this less satisfactory variety 
in the Tables of Permanent and Fugitive Pigments in 
the present volume as Vandyke brown B., the other kinds 
being called Vandyke brown A. It is unfortunate that 
the colour-value of the perishable variety is incom- 
parably greater than that of the more permanent sort. 

17 



258 CAPPAGH BROWN 

Cologne or Cullen earth, and Cassel brown or Cassel 
earth, are soft, impure varieties of brown coal or lignite. 
They vary in fixity, some of them being even more easily 
bleached by light than Vandyke brown B. ; these should 
not find a place on the palette of the artist. When 
slightly roasted, a part of the brown organic matter in 
these earths is charred or carbonized, and the substance 
becomes darker, duller, and decidedly less alterable by 
exposure. Some of the so-called Cologne earth now sold 
is merely Vandyke brown B., slightly changed by gentle 
roasting ; it is then rather less alterable. We have met 
with some specimens of Cassel earth which proved prac- 
tically permanent in oil, but even these faded quite 
distinctly when exposed to strong light after having been 
mixed with flake-white. 



Cappagh Brown : Euchrome — Mineral Brown. 

This earth was found on the estate of Lord Audley, in the 
Cappagh Mine, which was opened in the year 1814, and is 
situated about ten miles west of the town of Skibbereen, in 
the county of Cork. In composition and general characters 
it resembles raw umber, but has a more reddish hue. It 
contains ferric hydrate and ferric oxide, with a consider- 
able amount of one of the oxides or hydrates of manganese. 
It gives off a good deal of water when heated to 100° C, 
and acquires a rich reddish-brown colour, not unlike that 
of burnt sienna, and almost identical with that of Cale- 
donian brown. The specimens examined contained mere 
traces of organic matter, so that it cannot be regarded as 
a kind of bog-earth or peat, although it is, of course, 
possible that there may be another mineral found in the 
same locality which might be correctly so designated. The 



BISTRE 259 

following analysis represents the composition in 100 parts 
of a characteristic specimen of this pigment : 

Water, lost at 100° C. - 187 ^ Alumina - - - - 2-6 

Water, lost at a red heat - ii-6 | Lime - - - - - 11 

Iron oxide (Fe203) - - 34'4 j Silica - - - - - 4*6 

Manganese dioxide (MnOg) 27-2 | Phosphorus pentoxide(P205) 0-4 

It is probable that a part of the manganese really exists 
in the form of the red oxide (MngOJ, and a part of the iron 
as ferrous oxide (FeO). I have, however, calculated both 
these metals into their higher oxides. In this way it 
happens that the added percentages exceed 100, even when 
the traces of magnesia and potash present in Cappagh 
brown are not included in the total. The large quantity of 
water present in this mineral in a loosely-attached form 
(hygroscopic), amounting to nearly one-fifth of the weight 
of the pigment, indicates the desirability of cautiously 
drying the substance previous to grinding it in oil. A 
temperature of 60° C. should not be exceeded. 

Cappagh brown works well in oil, particularly if it be 
dried at a heat below that of boiling water before it be 
ground in oil. It is an innocuous pigment, but its perma- 
nence has scarcely been sufficiently tested. A rub of 
Cappagh brown in oil, exposed to strong sunlight for 
one month, lost a little of its yellow, assuming a some- 
what ruddier hue ; the change, however, was very slight, 
and did not appear to have increased after continued 
exposure for five months more. 

Bistre : Bister — Bvaunev Lack — Russhvaim. 

Bistre is prepared from the tarry soot of certain woods, 
especially from that of beech-wood, by the following pro- 
cess : The soot is finely ground and sifted, and then the 



26o ASPHALTUM 

powder is digested with successive portions of hot water 
until the latter no longer acquires a brown or yellow tint ; 
the residue is then ground with suitable quantities of gum- 
water and glycerin, and preserved in the moist state. To 
form cake-bistre the glycerin is omitted, but more gum is 
employed. Bistre is not used as an oil-colour. 

The tarry matter in bistre is its element of weakness. 
By exposure to strong light this tarry matter oxidizes, and 
the residual pigment becomes cooler in hue and paler. 
Professor Ogden Rood, experimenting with a weak water- 
colour wash of bistre, found that it lost 19 parts of its 
original intensity of 25 by an exposure of three and a 
half months to the summer sun. I have not found so 
considerable a change to occur with the samples of bistre 
which I have tried ; but this pigment varies much in 
composition, being obtained from the soot of different 
woods as well as from that of peat. The most fugitive 
preparations are those made from samples of soot con- 
taining the highest proportions of tarry matters. 

AsPHALTUM : Bitumen — Mineral Pitch — Antwerp Brown — 
Mummy — Mumie. 

Asphalt, asphaltum, or mineral pitch, has long been 
used as a pigment. The best known is that from the 
Dead Sea {Laciis asphaltites). Other abundant sources of 
this carbonaceous mineral occur in Trinidad ; Caxitambo 
and Berengela, in Peru ; Val de Travers, Neufchatel ; 
Avlona, in Albania, etc. 

Asphalt is rather a mixture of minerals than a single 
mineral ; it is, moreover, very variable in the nature, 
character, and proportion of its constituents. Essentially 
it consists of a number of liquid, semi-solid and solid, 
colourless hydrocarbons (related to the paraffins), asso- 



ASPHALTUM 261 

ciated with certain ill-understood dark-brown or black 
substances, v/hich constitute the useful part of the raw 
material. The best varieties for artistic use are those 
which contain the smallest proportion of the above- 
described hydrocarbons, for to the presence of these the 
treacherous character of asphalt as a pigment is due. On 
this account the hardest, most earthy and most brittle 
kinds should be chosen, and the crushed samples should 
always be submitted to a temperature of at least 250° C. 
before being ground in oil or turpentine. The operation 
of roasting native asphalt — keeping it over a slow fire 
* till it will boil no more and becomes nearly a cinder ' 
— was recommended by Williams in his ' Essay on the 
Mechanic of Oil-Colours' (1787), and furnishes a perfectly 
satisfactory and safe product. 

If carefully-selected asphalt be submitted to either of 
the processes named above, and then be moistened with 
spirits of turpentine, and ground in drying-oil (prepared 
with borate of manganese), a paint is obtained which 
neither cracks nor moves on the canvas like the unpurified 
material. Its fixity is further ensured by mixing it with a 
little copal varnish, and more particularly by associating 
it with a denser pigment, such as umber or flake-white. 
It is superior to the imitative asphalts made from coal- 
tar, now largely sold in lieu of the original and genuine 
product. The disadvantages attending the use of these 
coal-tar browns and of ordinary asphalt are two-fold. 
Not only are they treacherous on account of their easy 
fusibility, but they are liable to stain contiguous pigments 
by reason of their solubility in oil or varnish. When 
used successfully by the older artists they were always 
introduced sparingly, or were largely commingled with 
more solid paints. 



262 ASPHALT UM 

* Mummy,' as a pigment, is inferior to prepared, but 
superior to raw, asphalt, inasmuch as it has been sub- 
mitted to a considerable degree of heat, and has thereby 
lost some of its volatile hydrocarbons. Moreover, it is 
usual to grind up the bones and other parts of the mummy 
together, so that the resulting powder has more solidity 
and is less fusible than the asphalt alone would be. A 
London colourman informs me that one Egyptian mummy 
furnishes sufficient material to satisfy the demands of his 
customers for twenty years. It is perhaps scarcely neces- 
sary to add that some samples of the pigment sold as 
' mummy ' are spurious. Mummy was certainly used as 
an oil-paint at least as early as the close of the sixteenth 
century. 

Asphalt, after having been heated to drive off the 
hydrocarbons previously alluded to, cedes to ammonia a 
considerable quantity of a dark-brown colouring-matter, 
which in this way may be made available for water-colour 
painting. The ammoniacal solution is either evaporated 
slowly, to the consistence of a thick syrup, after the addi- 
tion of a little gum and glycerin, or it is precipitated with 
acetic acid, and the precipitate (after washing) is mixed 
with gum and glycerin, and then partially dried until it 
has acquired a suitable degree of consistency. But the 
water-colour paint thus made is not permanent. 

Merimee's process for preparing asphalt for use as an 
oil-colour cannot be recommended. He introduces shellac, 
white wax, and Venice turpentine into the mixture, as 
well as a large proportion of boiled linseed-oil. This 
preparation constitutes a very treacherous pigment. 



. PR USSIA N BRO WN 263 

Prussian Brown. 

This pigment, as usually met with in commerce, con- 
tains a considerable quantity of a soluble salt of potash, 
and is not fitted for the use of artists. But this impurity 
need not be present, as it may be removed by a thorough 
washing of the powdered colour with boiling water. A 
still better plan is to prepare Prussian brown from one 
of those varieties of Prussian blue which contain no 
potassium. It is made by throwing small pieces (the size 
of hazel-nuts) of Prussian blue upon a plate of iron main- 
tained at a red heat. Each fragment burns hke tinder, 
and if care be taken to employ the right heat for the 
proper time, will show a mixed hue, partly yellowish 
brown, partly reddish brown, and partly black. The 
product, still hot, is thrown into water, ground, washed, 
and dried. Prussian brown thus made has a rich 
colour of considerable translucency and good drying 
character. In hue it is warmer than asphalt. It is quite 
permanent. 



CHAPTER XIX 

BLACK PIGMENTS 

Indian Ink : Chinese Ink — Japanese Ink — Encre de Chine 
— Chinesische Tusche, 

This ink has been prepared in China for at least 2,000 
years. It consists essentially of a very fine lamp-black, 
associated with gelatin, and scented with musk, camphor, 
cloves, or rose-water. The lamp-black employed is 
derived from the imperfect combustion of oil or of pine- 
wood. The oils chiefly used are those of Sesamum indi- 
cum, Cannabis sativa, and Dvyandria cordata ; but in some 
factories rape-oil, bean-oil, or the oil of Gleditschia sinensis 
is employed. According to the treatise of Chen-ki-suen, 
which was written a.d. 1398, these oils are burnt in 
small earthenware lamps in the presence of a limited 
supply of moist air. The smoke is collected in earthen- 
ware conical covers; from these the condensed soot is 
removed at short intervals, care being taken to preserve 
those portions only which are free from tarry products. 
The soot is finally sifted, and reduced to an extremely 
fine powder. Lac-resin, rock-oil, as well as many kinds 
of wood, have been employed for the preparation of this 
carbonaceous basis of China ink in different parts of the 
empire, and at different times. It would appear that 
from all of these combustibles, if due care be taken, an 

264 



INDIAN INK 265 

excellent product may be obtained. The next step in 
the manufacture consists in the incorporation of the soot, 
prepared as above described, with the necessary amount 
of size. The size employed should be made from a 
mixture of clean fish-glue and parchment-size; this is 
thoroughly mixed, while warm, with the fine soot. The 
paste thus formed is made into balls, which are heated 
for some time at the temperature of boiling water, and 
then fashioned roughly into sticks. These are subjected 
to repeated blows — some hundreds, at least — from a 
hammer; they are re-heated occasionally during this 
operation, in order to prevent them from becoming hard. 
The perfume, consisting of musk and camphor, mixed 
with a little rose-water, is incorporated with the mass. 
The material, after further pounding and beating, may 
then be pressed into the wooden moulds which are to 
give it its final form. A tedious process of drying 
follows next, the sticks of ink being finally packed in 
the ash of rice-straw frequently renewed. After the 
removal of adhering ash, the sticks are cleaned, gilt or 
otherwise ornamented, and polished with an oily brush. 

If the soot used in the manufacture of this ink be con- 
taminated with tarry or empyreumatic matters, it yields 
a brownish-black product ; the purer and the finer the 
state of division of the carbon, the more intense is the 
black, and the more neutral are the greys which it yields 
on dilution with water, or by admixture with opaque 
white pigments. 

There are many qualities of this ink made in China. 
The best kinds are hard and homogeneous ; they show a 
lustrous black fracture, and, when rubbed with water, 
do not give rise to the separation of any curdy particles. 
Those having, in tint with water, a bluish or violet tinge 



266 INDIAN INK 

are the most esteemed ; the pure black come next, and 
the brownish or yellowish black last. 

A stick of Indian ink should be rubbed on the palette, 
in straight lines, backwards and forwards. A very con- 
venient ink-slab for this purpose forms part of the fittings 
of the Japanese writing-case or box, called ' suzuri-bako.' 
It consists of an oblong block of dark slate, in which a 
sloping cavity has been hollowed out. The slight 
* tooth,* or roughness of the surface, greatly helps the 
rubbing-down of the ink. A strong wash of this ink, on 
sized paper, should not be affected, when once dry, by 
having water brushed freely over it. Bluish-black and 
pure black Indian ink is permanent under prolonged 
exposure to sunlight or impure air ; but the brownish 
varieties become paler, less brown, more neutral, by 
the action of light. Like most carbonaceous matters, 
Indian ink occasionally tends to absorb to a small 
extent some of the organic pigments which may be 
brought into contact with it in the process of colouring a 
drawing. 

Indian ink is available for tempera-painting, but can- 
not be used with oil. 

Indian ink has been imitated with fair success in 
France. The chief difficulty in preparing it seems to 
lie in the preparation of a suitable gelatinous medium 
with which to mix the purified lamp-black. A size 
prepared from washed fish-glue (by partial precipitation 
with tannin, and subsequent solution of the precipitate 
in more size) affords a good binding material. The size, 
in true Chinese ink, forms a very large part of the total 
weight, varying from one-fourth to over one-third ; but 
the European imitations rarely contain as much. Japan- 
ese ink is generally inferior to Chinese. 



LAMP-BLACK 267 

Chinese amateurs sometimes form collections of rare 
and old kinds of Chinese ink, occasionally giving for 
sticks bearing the marks of renowned makers not less 
than their weight in gold. Such specimens are prized 
for their rarity, not on account of any special merits 
as pigments which they may possess ; and a Chinese 
ink collector regards it as an unpardonable offence to 
moisten any of his specimens with a view to testing their 
quality. 

Lamp-Black : Noiv de Lampe — Noiv de Fumee — Noiv de 
Houille — Rnss — L ampenschwavtz. 

When resins, resinous woods, fatty oils and fats, 
paraffin and paraffin oil, or coal-tar oils, are burnt with 
an insufficient supply of air, a considerable part of the 
carbon they contain may be deposited in the form of soot. 
This soot is not, however, pure carbon, but retains 
variable proportions of the tarry products of imperfect 
combustion or destructive distillation ; these impart to 
lamp-black a more or less pronounced warm brownish 
hue, except in the cases in which it has been prepared 
by processes specially devised to intercept the tarry 
and oily products in question. Sometimes small fur- 
naces, sometimes large lamps with long wicks are 
employed in its manufacture, the soot given off being 
collected in two or more receivers ; the soot first de- 
posited contains the larger part of the impurities. This 
point may be illustrated by the simple experiment of 
depressing a white porcelain plate into the flame of a 
candle ; the nearer the plate to the wick, the browner 
will be the soot deposited. 

Lamp-black carefully made is an unalterable pigment ; 



268 CHARCOAL-BLACK 

but its employment for pictorial purposes has frequently 
been objected to by writers on artistic practice as 
tending to heaviness and opacity in the shadows. 
With the exception of a few pigments of organic 
origin, which in water-colour painting have a tendency 
to cede some of their colouring matter to any kind 
of carbonaceous black, lamp-black exerts no injurious 
influence upon any pigments which are stable when used 
alone. 

Numerous carbonaceous substances have been used as 
black or brown-black pigments. Amongst these anthracite 
and common bituminous coal may be named. Van Man- 
der and De Mayerne both mention forge or pit coal. Black 
shales and black slates have long been employed in the 
preparation of dark grey pigments. These minerals owe 
their colour in part to carbon or compounds of carbon, 
in part to very finely divided iron pyrites. They are 
permanent, so far as the carbon present is concerned. 

Charcoal-Black : Blue-Black — Vine-Black — Frankfort- 
Black — Noir de Vigne — Rehschwartz. 

When non-resinous woods and woody tissues are 
strongly heated in crucibles or other almost completely- 
closed vessels, the residue contains the greater part of the 
carbon of the original material, and preserves its form. 
As the charcoals thus made contain some soluble mineral 
matter, particularly potash salts, they should be coarsely 
ground and thoroughly washed with hot water previous to 
their being finally converted into paints. They are also 
hygroscopic, and therefore need to be dried before being 
ground in oil. 

Amongst the best materials for producing these char- 
coal or vegetable blacks may be named the hard shells or 



. CHARCOAL-BLACK 269 

stones of plums, almonds, and similar fruits; coco-nut shell 
broken into small pieces; cork cuttings, and the twigs of 
beech and shoots of vine. Coco-nut yields the densest, 
most velvet-like black; vine-shoots a less solid black, 
having a bluish hue. Washed wine-lees yield a rich black 
— Frankfort-black. 

When charcoal has been prepared at a sufficiently high 
temperature, and then has been thoroughly washed, there 
is no question as to its permanence as a pigment in all 
media. But if it retains tarry matters, or has been im- 
perfectly carbonized, then it may become greyer or less 
brown (when used in thin washes) after long exposure to 
Hght. This change is due to the oxidation of the tarry 
matters, or of the brown substances which are interme- 
diate in composition between the original vegetable 
materials and the carbon, which is the final product of 
their torrefaction out of contact with the air. And one 
peculiar property, possessed in varying degrees by char- 
coal of every kind, must not be lost sight of. Charcoal 
withdraws the majority of organic colouring matters from 
suspension, and even from solution in water. A pale tint 
of rose-madder in water, if a pinch of coco-nut or vine- 
black be added, becomes rapidly decolourized, the pig- 
ment being completely absorbed, although not really 
destroyed. Animal charcoal (bone-black, ivory-black) 
exerts a still more energetic action of this character; 
but lamp-black is less powerful. 

It is to be regretted that the beautiful bluish blacks, 
derived from such materials as the shoots of the vine and 
beech, are frequently fraudulently imitated by mixtures of 
lamp-black and indigo. The purple vapours of indigotin, 
given off when such a mixture is heated in a test-tube, 
betray the adulteration at once. 



270 IVORY BLACK 

Ivory Black : Noiv d'lvoive — Elfenheinschwartz. 

Waste ivory, in the form of turnings, shavings, and saw- 
dust, if charred in closed vessels, leaves a black residue, 
which, however, consists essentially of bone-earth (calcium 
carbonato-phosphate), stained by the presence of a few per 
cents, of carbon. On exposure to the air, ivory black 
absorbs, not only the gases of the atmosphere, but also a 
very considerable proportion of moisture. On this account 
ivory black, just previous to its being ground in oil, should 
always be thoroughly dried. As this substance has a strong 
decolourizing power when placed in contact with moist 
organic pigments, it is better adapted for use in oil paint- 
ing than with water colours. This decolourizing property 
belongs also to the animal blacks obtained by charring 
horn and bone shavings — products which are frequently 
substituted for genuine ivory black. Sir Charles Eastlake 
tells us that in a collection of specimens of water-colour 
tints inserted in the Mayerne manuscript the 'hartshorn* 
black, made from covnu cervinum, remains very intense. 

Ivory and bone black are perfectly permanent black 
pigments ; the latter is quite free from the bluish tinge 
which characterizes most of the vegetable charcoals. 
Both are better adapted for oil than for water-colour 
painting, for which vine black is preferable. 

Black Lead : Plumbago — Graphite — Graphit. 

The material of which so-called black-lead pencils are 
made is essentially nothing but one of the three forms in 
which the element carbon occurs ; diamond is another ; 
lamp-black may be taken as a good representative of the 
third form. Graphite is the most appropriate name for 
the mineral commonly known as black lead, but which 



GRAPHITE 271 

in reality contains no lead, and is in no way related to 
that metal. Graphite was found of good quality at 
Borrowdale in Cumberland, a locality which has been 
stated, probably erroneously, to be now exhausted ; but 
excellent supplies of this mineral come from the Albert 
Mine, Siberia, Mount Alibert in the Ural, Ceylon, and 
many other places. Graphite, however, is never found 
in a state of perfect purity, always leaving, when burnt, 
some incombustible matter or ash. 

In order to prepare graphite for use as a pigment, the 
purest pieces should be selected ; these should be at first 
broken into small fragments in order that obviously con- 
taminated bits may be rejected before the material is 
ground. Inferior qualities of graphite may be purified 
by being coarsely ground, and then heated with strong 
hydrochloric acid to remove iron and alumina. After 
washing, the thus-far purified material should be placed 
in a leaden or platinum vessel and gently warmed with 
a solution of hydrofluoric acid to remove silica. The 
graphite, after this treatment, is to be washed with 
abundance of water, and ground to a very fine powder, 
which is then ready for admixture with gum water or, 
after drying, with oil. The addition of a little china clay 
during the grinding of graphite in oil tends to produce a 
more manageable paint. 

Graphite has a very dark-grey colour, and forms pure 
tints of grey with white pigments. It is equally well 
adapted for use in water-colour, oil, fresco, and tempera 
painting. It is absolutely permanent, and without action 
on other pigments. 

Graphite is sometimes adulterated with charcoal or 
lamp-black. When a very thin layer of the suspected 
pigment — freed from oil or other vehicle — is spread on a 



272 SEPIA 

piece of platinum foil and strongly heated over a lamp^ 
the lamp-black will burn away, leaving the true graphite 
unaltered. If a change of hue or tint occurs, this is a 
sign of the presence of the above-named adulterant. 

Sepia. 

The dark-brown colouring-matter from the ink-bag of 
Sepia officinalis, Loligo tunicaia, and other species of cuttle- 
fish common in the Mediterranean and Adriatic, has not 
been thoroughly investigated from a chemical point of 
view. The pure pigment, which constitutes four-fifths 
of the weight of the dried ink-bags as they occur in com- 
merce, partakes of the character of a weak organic acid, 
and is soluble in alkalies and precipitated by acids. In 
preparing the substance for artists' use, it is commonly 
first removed from the sacs containing it, dissolved in 
soda or ammonia solution, and then, after straining the 
solution, thrown down by neutralizing the alkali with 
hydrochloric acid ; the precipitate is then washed by de- 
cantation, and dried. Sometimes the filtered ammoniacal 
solution is used directly as a liquid ink. The chief 
impurities of the natural sepia are salts of lime and 
magnesia, which may be partly removed by washing the 
dried and crushed sepia first with dilute hydrochloric 
acid and then with water, previous to dissolving it. 

Sepia is of a redder or warmer brown hue than bistre, 
but it is not so reddish as Vandyke brown. Of these 
three pigments, there is no question that sepia is the least 
alterable. It is not, however, permanent when exposed 
to sunshine, although in darkness or in diffused daylight 
it suffers no appreciable change either in depth or quality. 
It might, indeed, have been supposed that sepia would 
prove unalterable, from the consideration of the observed 



SEPIA 273 

fact of the pigment from the ink-bags of fossil cuttle-fish 
showing now, when used as a water colour, the same 
hue and the same chemical characters as recent sepia 
from the Mediterranean cuttle-fish of to-day. But it 
must be recollected that this fossil pigment has been 
excluded completely from the adverse influence of light, 
and in great measure from that of air, during the long 
ages which have elapsed since it was embedded in rock. 
And it is light which, in the case of the majority of 
organic pigments, is the determining cause of the changes 
brought about by the combined presence of moisture and 
atmospheric oxygen. 

Sepia is not employed as an oil colour. 

There are several grey pigments which, being com- 
pounded of other paints already described, need hardly 
be mentioned here. Amongst these are neutral tint and 
Payne's grey, which in water-colour are still prepared 
by commingling indigo, crimson lake, and ivory black, 
but which have been replaced in oil by artificial ultra- 
marine, ochre and ivory black — an entirely trustworthy 
mixture. Slate grey, prepared from a rather soft and 
very dark-coloured slate, is a satisfactory pigment both 
in artistic quality and in stability. 



18 



CHAPTER XX 

CLASSIFICATION OF PIGMENTS 

The painter naturally classes pigments according to their 
colour, or more exactly according to what are called the 
constants of colour — namely, hue, brightness and purity. 
He also takes into account transparency and opacity, 
although these terms are conventional and comparative 
only, since no pigment is perfectly transparent, none 
perfectly opaque. Another basis of classification, and a 
very important one, that of stability, will be considered 
in the next chapter ; at present we are concerned with 
none of these methods of grouping pigments, but with 
others founded either upon their origin, or their physical 
characters, or their chemical composition. 

Pigments are often classified into two groups — the 
mineral, and the organic. It is necessary to divide these 
groups further, in some such way as this : 

( Natural : as ochre, terre verte, ultramarine. 
Mineral Pigments, i . ^-c • i ,• • •.• u i*ui 

I Artincial : as aureolin, vindian, cobalt blue. 

/ Animal : as Indian yellow, carmine, sepia. 

Organic Pigments, j Vegetable : as gamboge, sap green, indigo. 

' Artificial : as Prussian blue, verdigris. 

Such -a classification brings into prominence one 
marked distinction between the two groups, for, in 
accordance with one's expectation, the mineral pigments 

274 



CLASSIFICATION OF PIGMENTS 275 

are, as a rule, characterized by a much higher degree of 
permanence than those of organic origin. [The chemist 
looks upon all compounds containing carbon, save the 
carbonates, as organic; but at the same time the dis- 
tinction between organic and inorganic, or organic and 
mineral, is nothing more than a convenient convention.] 

Other bases of classification are afforded by physical 
or mechanical characters. Pigments may be fixed or 
volatile, soluble or insoluble, crystalline or amorphous, 
substantive or adjective. There are difficulties in carry- 
ing out these schemes of classification, and it will be 
found that distinctions of physical character are utilized 
to the best purpose when connected with such a chemical 
classification as is offered below. 

The simplest chemical classification is this : 

Elements ; as graphite, lamp-black, gold. 
Compounds ; as aureolin, viridian, vermilion. 
Mixtures ; as yellow ochre, brown pink, rose madder. 

After considerable expansion and some rearrange- 
ment, the differences just indicated afford a reasonable 
basis for a chemical classification which will prove of 
real service in judging of the degrees of stability, and of 
the possible interaction of pigments."*^ The mixed and 

* In a pamphlet by M. Paul de Lapparent there is an ingeniously 
constructed diagram giving, at one view, a list of pigments which, 
in the judgment of the author, react upon one another. If we omit 
from the list red lead, we shall be able to cancel nearly one-third 
of the black marks assigned to mixtures of two pigments ; but we 
shall still include two conspicuous offenders, namely, pale cadmium 
and Prussian blue. Pale cadmium is stated to be incompatible 
with Indian red, Venetian red, burnt sienna, the native earths, 
ivory black, Prussian blue, and cobalt violet ; while Prussian blue 
is marked as affecting, or as affected by, Venetian red, burnt sienna, 
deep cadmium, orange cadmium, pale cadmium, aurora yellow. 



276 



CLASSIFICATION OF PIGMENTS 



even indefinite character of many pigments, and the 
chemical solitariness of others, preclude the formation of 
groups having equal rank and precise group-characters : 
thus the proposed chemical classification, though con- 
venient, has no pretension to completeness. I suggest 
the following nine groups : 

Group I. — Elements 
Sih^er. 
Gold. 
Platinum. 



Ivory black 
Charcoal black 
Lamp black 
Indian ink 
Graphite 



■Contain carbon. 



Aluminium. 



Zinc white - 

Green oxide of 

chromium 

Burnt umber 

Cobalt green 
Cobalt red - 
Cobalt blue - 



Group II. — Oxides 

- ZnO. Coeruleum 
Red lead - • 
Venetian red 

Oxides of Fe Light red 
and Mn. Indian red 

- CoO,«ZnO. Burnt sienna 

- CoO.wMgO. 

- CoOjHAUOg. 



- CoO.nSnOs 

- Pb304. 



■Chiefly FegOg. 



Group III. 
Cadmium yellow - • - CdS. 
Kings' yellow . . - - AsgSg. 

Realgar - AsgSa. 

Vermilion HgS. 



-Sulphides 
Ultramarine 
Artificial ultramarine 
Green ultramarine 
Red ultramarine 




the native earths, ivory black, white lead, zinc white, and viridian. 
On the other hand, M. de Lapparent allows that vine black is an 
entirely innocuous and permanent pigment. My experience is not 
in general agreement with the judgments of M. de Lapparent as 
embodied in the diagram under consideration. For instance, I do 
not find that aureolin reacts with white lead or with ultramarine, 
nor can I admit that Prussian blue deserves the bad character 
assigned to it. Possibly the purity of the particular pigments with 
which our author dealt was not assured in all cases. Might there 
not have been free sulphur in his pale cadmium and free acid in his 
Prussian blue ? 



CLASSIFICATION OF PIGMENTS 



277 



Yellow ochre 

Raw sienna 
Raw umber 



Group IV.— Hydrates 



FeaOg.wHaO. 

Oxides and hy- 
drates of Fe 
and Mn. 



Emerald oxidej^, q j^ q^ 

of chromium; 
Mountain blue - CuU^O^. 



Flake white 
Whitening 



Group V. — Carbonates 



2PbC03,PbH202. 
CaCOo. 



Chessylite 
Malachite 



CuC03,CuH202. 
aCuCOg.CuHgOg. 



Group VI. 

/Silicate of Fe, K, 
I Mg. 
Egyptian blue CuO,CaO,4Si02. 



Terre verte 



-Silicates 
Smalt 



f Silicate of Co 
I and K. 



Baryta yellow - 
Strontia yellow 
Chrome yellow 



Group VII. — Chromates 

- BaCrOj. I Chrome red - 

- SrCr04. I Zinc chromate 

- PbCr04. I 



ZnCrO^. 



Group VIII.— Various Inorganic Salts 



Baryta white 
Lead sulphate 
Aureolin - 
Naples yellow 



BaS04. 
PbS04. 
KfiCogiaNOg. 
Contains Pb, 
Sb, O. 



o u • r X /"Contains 

Schwemfurt greenj ^u, As. O. 

_ ^ f Chromium 

Tungsten green | t„„g,t^,. 

Manganese violet | ^ , 

XT" 1- • 1 .-^ metaphos- 

= Nurnberg violet , / 

^ I pnate. 



Group IX.— Organic Compounds 



Indian yellow. 
Yellow lake. 
Gamboge. 
Pure orange. 
Rose madder. 
Madder carmine. 
Rubens madder. 
Madder red. 
Purple madder. 



Brown madder. 
Scarlet alizarin. 
Crimson alizarin. 
Carmine. 
Crimson lake. 
Scarlet lake. 
Purple lake. 
Sap green. 
Verdigris. 



Emerald green. 

Indigo. 

Prussian blue. 

Antwerp blue. 

Bitumen. 

Bistre. 

Sepia. 

Vandyke brown B. 



278 SULPHIDES 

One of the chief lessons to be learnt from this 
classification is this, that the members of each class, as 
a general rule, exert no action upon one another. This 
is explained easily. The oxides of Group II., having 
already taken up the full complement of oxygen which 
they can acquire under ordinary conditions, are not likely 
to be oxidized by admixture with other oxides of similar 
character. In the same manner the sulphides of 
Group III. neither give sulphur to, nor receive it from 
the other sulphides, for all but one of them have been 
produced in the presence of excess of sulphur. The 
following characteristics of each group may prove useful 
in the study of their chief members : 

Group I. : Elements. — All the black pigments in 
ordinary use consist of or contain the element carbon, 
and are not subject to change : graphite is a form of 
carbon and is unalterable and inert. Gold, if pure or 
nearly free from alloy, is not liable to chemical change, 
but silver readily tarnishes by combining with sulphur ; 
drawings in silver-point are frequently found to have 
altered in hue from this cause. The best metal-point for 
fine drawing is pure platinum. 

Group II. : Oxides. — These have generally been 
prepared at a high temperature, and are not easily 
amenable to chemical or physical change : they are, 
moreover, not liable to affect other pigments, being 
practically inert. 

Group III. : Sulphides. — Some of these may give up 
sulphur to the metallic bases of other pigments. Thus 
cadmium yellow blackens emerald green, producing 
copper sulphide. One of these pigments, vermilion, is 
prone to a molecular change, whereby the red crystalline 
form passes, without chemical alteration, into the black 
amorphous variety. The members of this group some- 



VARIOUS INORGANIC SALTS 279 

times contain free sulphur, or injurious sulphur com- 
pounds. 

Group IV. : Hydrates. — The water present in these 
compounds exists in two states, essential and hygro- 
scopic. Sometimes a part of the former may be lost, and 
a change of hue occur in consequence, but the alteration 
is rare, save in the pigments which owe their colour to 
the presence of copper hydrate. In the case of raw 
umber, the water present acts rather in aiding the oxygen 
of the air, under the influence of sunHght, to oxidize 
some of the peaty or bituminous matter sometimes 
present in this pigment. 

Group V. : Carbonates. — Three out of the four 
carbonates included in this group are liable to suffer 
change on account of the metal they contain (lead or 
copper) combining with sulphur, and so forming a brown 
or black sulphide. 

Group VI. : Silicates. — These are generally inert 
bodies little prone to suffer or cause change. Some of 
the ochreous earths contain silicates of iron, manganese, 
and alumina, as well as the hydrates of the two former 
metals, and so might be placed in this group. 

Group VII. : Chromates. — This group consists of 
compounds rich in oxygen. When in contact with some 
of the more alterable organic pigments belonging to 
Group VIII. the chromates occasionally lose oxygen. 
On this account they show a tendency to acquire a 
greenish or greyish hue, the result of the reduction of 
the red oxide of chromium to the green oxide. This 
change is accompanied by a corresponding injury to the 
colour of the organic pigment which has been involved 
in the reaction. 

Group VIII. : Various Inorganic Salts. — A num- 
ber of miscellaneous compounds having no chemical 



28o 



CLASSIFICATION OF PIGMENTS 



relationship have been thrown into this group. One, a 
sulphate, is insoluble and inalterable ; another, potassium 
cobalti-nitrite, is generally inert, but, owing to its nitrous 
constituent, acts injuriously upon some organic pigments, 
notably on indigo. The members of the group which 
contain lead or copper may darken in the presence of 
sulphuretted hydrogen and of some other sulphur com- 
pounds. 

Group IX. : Organic Compounds. — This group in- 
cludes many more pigments than any other : not one of 
its members possesses the permanency belonging to the 
majority of the mineral pigments, while some are so 
fugitive that they may even be used for producing a 
photographic picture by being exposed to sunlight under 
a negative. This fading is generally due to the com- 
bined action of water and oxygen : in oily and resinous 
media it is lessened, retarded, or even prevented by the 
hydrofuge character of these vehicles. 

It should be noted that members of each group, 
though presenting one or more characters in common, 
often exhibit certain chemical and physical differences of 
deportment. Here is a list of the chief changes which 
they are capable of suffering, with illustrative examples : 



Molecular rearrangement 



Subsidence 
Volatilization 
Solution ... 
Fusion 
Oxidation ... 
Reduction . . . 



Sulphuration 



VermiHon ; cadmium sul- 
phide. 
Smalt. 

Kings' yellow. 
Strontia yellow ; aureolin. 
Asphalt. 

Carmine ; Vandyke brown. 
Naples yellow ; chromates. 
White lead ; emerald green. 



CLASSIFICATION OF PIGMENTS 281 

The effect of pulverization upon pigments may be 
mentioned in this connexion. Generally, the more 
finely an alterable pigment is ground, the more suscep- 
tible does it become to chemical injury : its colour 
becomes at the same time paler, and may even change 
in hue as well as in tone. Continued grinding, beyond 
the degree necessary to develop the proper colour, im- 
proves some pigments, but injures others. 

In the chemical classification of pigments which has 
been sketched in the present chapter there comes out in 
rather striking relief one point to which no allusion has 
yet been made. It is indeed a point which touches the 
chemist rather than the artist, and yet it seems to merit 
a passing reference in this place. I refer to the number 
of gaps in the table — to the number of elements and of 
classes of salts which have no place therein. The 
scientist will not, indeed, expect to find amongst these 
9 groups any substances possessed, to a marked degree, 
of the property of solubility in water, for he will recog- 
nise the unfitness of such bodies for use as paints. But 
he will probably observe, with some surprise, that there 
are no compounds of fluorine, chlorine, bromine, or iodine 
in our lists, but two sulphates, only one substance con- 
taining tungsten, and not one containing nickel, uranium, 
molybdenum, or vanadium. Coloured insoluble com- 
pounds indeed exist of all these elements ; several of such 
compounds have been proposed and even employed as 
pigments, but instability or injurious action upon other 
pigments has banished these candidates from the palette 
of the artist. 

A few words may be added here as to the distinction 
between substantive and adjective pigments. Of the 
former class aureolin, vermilion and malachite may be 



282 CLASSIFICATION OF PIGMENTS 

cited as examples ; to the latter all the lakes belong. 
Substantive pigments are homogeneous, definite sub- 
stances, simple or compound, but not separable into two 
bodies, having differing optical qualities. On the other 
hand, adjective pigments contain two substances, one 
coloured, and another generally colourless, through which 
the former is disseminated or over which it is extended 
as on a background. 



CHAPTER XXI 

TABLES OF PERMANENT, FUGITIVE, AND ALTERABLE 
PIGMENTS 

By several different methods, data may be obtained which 
enable us to classify pigments — roughly, it is true — in 
accordance with their varying degrees of stability. Such 
data are derived partly from the known chemical and 
physical constitution of the various substances; partly 
from a study of old paintings and drawings in which they 
have been used ; and partly from special experimental 
tests of permanency to which they have been subjected. 
Selections from these data are given in Chapters XX., 
XXIV., and XXVI., of the present work ; but much 
additional information has been furnished by other trials, 
conducted by the author and other experimenters, for 
which space could not be found in this volume. Tables 
constructed from such data must not be regarded as 
affording exact values, but merely approximations. From 
some minute and often obscure cause differences of deport- 
ment, under exposure to hostile influences, will occasion- 
ally be observed in the case of two specimens of the same 
pigment having the same hue. And, further, the group- 
ing of pigments into a small number of classes is a 
conventional and convenient arrangement which cannot 
accurately represent the numerous degrees of stability or 
instability which characterize the several pigments under 

283 



284 



TABLES OF PIGMENTS 



discussion. For when we leave the practically unalter- 
able mineral pigments, we have to deal with a number of 
preparations which fall by irregular and often barely recog_ 
nisable steps from the almost permanent to the hopelessly 
fugitive. One example of this difficulty in classification 
must suffice : aureolin is almost worthy of a place in 
Class I., Indian yellow scarcely deserves inclusion in 
Class II. The action of mixed pigments upon one another, 
though not as frequent as it is supposed to be, creates 
another difficulty in our classification, so also does the 
medium employed in painting, which may either protect 
an alterable pigment from change or aid in its destruction. 
In fact, each method of painting, if really distinct, requires 
a special classification of the pigments to be employed in 
carrying it out. 

In the annexed classification, a limit of three orders of 
stability has been adopted, the first class including the 
practically permanent pigments ; the second class those 
which, though liable to a variable measure of change, may 
yet generally be allowed ; and the third class those which 
should be definitely excluded from the palette : 



CLASSIFIED TABLE OF PIGMENTS FOR OIL-PAINTING 
Class I Class II Class III 



Baryta white. 
Zinc white. 
Flake white. 

Yellow ochre. 
Raw sienna. 
Baryta yellow. 
Naples yellow. 
Cadmium orange. 



White 



Yellow 
Aureolin. 
Indian yellow. 
Strontia yellow. 
Chrome yellow. 
Cadmium yellow. 



Kings' yellow. 
Yellow madder. 
Brown pink ; yellow 

lake. 
Gamboge. 
Zinc chromate. 



TABLES OF PIGMENTS 



28s 



Class I 

Vermilion. 
Indian red. 
Light red. 
Venetian red. 
Red ochre. 



Cobalt violet. 
Mars violet. 
Violet ultramarine. 

Emerald oxide of 
chromium. 

Green oxide of chro- 
mium. 

Cobalt green. 

Green ultramarine. 

Ultramarine. 
Artificial ultra- 
marine. 
Cobalt. 
Coeruleum, 

Burnt sienna. 

Raw and burnt um- 
ber. 

Cappagh brown. 

Verona brown. 

Prussian brown. 

Vandyke brown A. 
(earthy). 

Ivory- black. 

Charcoal-black. 

Lamp-black. 

Graphite. 



Class II 

Red 
Madder carmine. 
Rubens' madder. 
Rose madder. 
Madder red. 
Purple madder. 
Scarlet lake (ali- 
zarin). 

Violet 
Manganese violet. 



Green 
Emerald green. 
Terre verte. 
Malachite. 
Madder green. 



Blue 
Smalt. 

Prussian blue. 
Antwerp blue. 
Chessylite. 

Brown and Black 
Madder brown. 
Cologne earth. 



Class III 

Crimson lake. 

Carmine and burnt 
carmine. 

Indian lake. 

Scarlet lake (cochi- 
neal) . 

Purple lake. 

Violet carmine. 



Verdigris. 
Sap green. 
' Green vermilion, 

etc. 
Green verditer. 



Indigo. 
Blue verditer. 
Blue ochre. 



Vandyke brown B. 

{bituminous). 
Bistre. 
Sepia. 
Bitumen ( = asphalt). 



286 TABLES OF PIGMENTS 

In order to adapt the foregoing classified table to water- 
colours, some changes and additions must be made. 
Flake white, Naples yellow (true), cadmium (pale), and 
vermilion (artificial), must be removed from the Class (I.) 
of permanent pigments and placed in Class III., to which 
also must be relegated several pigments from Class II., 
namely, chrome yellow, malachite, and madder brown. 
Of course, it should be clearly understood that no pigment 
belonging to Class III. should be employed in artistic 
painting. One satisfactory addition, and one only, can 
be made to Class I. in the table. Indian ink is a pigment 
available for water-colour painting, and when it is free 
from a brownish hue may be safely used. Bistre and 
sepia are likewise used only as water-colours, but they are 
both fugitive, and must be placed in Class III. Almost 
the same modifications of the table are required in the 
case of tempera-painting as in water-colour painting. 
With fresco-painting the exclusion of many more pigments 
is an absolute necessity, as they are completely ruined by 
caustic lime. Not only are all the chromates inadmissible, 
as well as all the pigments which cannot be trusted as 
water-colours, but likewise Prussian blue and Antwerp 
blue, while the madder colours are much altered in hue 
when used in this process. In stereochromy the number 
of available pigments is still further reduced. 

It may not be uninstructive if we cite in this place the 
classification of pigments as used in oil which M. Decaux 
has published. The order followed by this experimenter 
is that of stability ; the figures prefixed to the names of 
the individual pigments indicate the degree of perma- 
nence, I marking out the materials which are quite 
unchangeable, while 45 is the most fugitive of all : 



TABLES OF PIGMENTS 



287 



DECAUX'S TABLE OF PIGMENTS FOR OIL-PAINTING 



I. Zinc white. 

I. Flake white. 

I. Yellow ochre. 

I. Naples yellow. 

I. Cadmium (deep). 

I. Raw sienna. 

I. Red ochre. 

I. Mars red. 

I. Venetian red, 

I . Burnt Italian earth. 



Class I 

I. Green oxide of chro- 
mium. 
I. Ivory black. 
I. Terre verte, 
I. Green ultramarine. 
I. Cobalt blue. 
I. Artif. ultramarine. 

1. Ivory black. 

2. Mars brown. 

3. Burnt sienna. 



4. Cobalt green. 

5. Mars yellow. 

6. Mars orange. 

7. Burnt umber. 

8. Viridian. 

9. Indian red. 

10. Mars violet. 

1 1 . Indian yellow. 

12. Emerald green. 



13. Malachite green. 

14. Scheele's green, 

15. Raw umber. 

16. Vandyke brown. 



Class II 

17. Prussian blue. 26. Madder ' rose 

18 to 23. Various madder doree. ' 

lakes. 27. Brown madder. 

24. Madder carmine. 29. Cassel earth. 









Class III 






30. 


Pale chrome. 


35. 


Asphalt. 


43. 


Yellow lake. 


31. 


Zinc chromate. 


36. 


Brown pink. 


44. 


Carmine. 


32. 


Pale cadmium. 


38. 


Vermilion. 


45- 


Crimson lake. 


33- 


Orange chrome. 


42. 


Burnt carmine. 







On comparing this classified list with that previously 
given a general accordance will be perceived, the low 
position given to raw umber and to vermilion, as well as 
the very high place assigned to Indian yellow and to 
terre verte, constituting the chief exceptions. 

In closing this chapter it may be useful to state that 
the pigments to which a place in our Class I. has been 
assigned have stood the very severe test of long exposure 
to direct sunlight. On a subsequent page it will be shown 
that this method of determining the stability of pigments 



TABLES OF PIGMENTS 



is not in all cases a fair one, because changes brought 
about by such exposure may not occur at all when the 
temperature does not rise beyond a particular point, and 
when the radiant energy of light and actinism does not 
exceed a moderate measure of intensity. So far, then, as 
exposure to light is concerned, it may happen that some 
of the pigments in Class II. really deserve a higher posi- 
tion than that assigned to them in our table. In this 
connexion we may give some of the conclusions which 
Messrs. Winsor and Newton have published as to the 
stability of oil colours when exposed, not to sunshine, but 
to a strong north light. It will be noticed that the class 
of permanent pigments has been greatly enlarged as the 
result of the milder ordeal through which the materials 
have passed : 

Class I. — Permanent 



Zinc white. 
Aureolin. 
Cadmium yellow. 
Yellow ochre. 
Raw sienna. 
Baryta yellow. 
Mars yellow. 
Vermilion. 
Venetian red. 
Light red. 
Indian red. 
Alizarin lakes. 
Crimson madder. 



Madder carmine. 
Pink madder. 
Rose madder. 
Purple madder. 
Brown madder. 
Rubens' madder. 
Scarlet lake (new). 
Burnt lake (madder). 
Cobalt green. 
Oxide of chromium. 
Viridian. 
Cerulean blue. 
Cobalt blue. 



Ultramarine. 
Manganese violet. 
Cobalt violet. 
Prussian brown. 
Caledonian brown. 
Cappagh brown. 
Burnt umber. 
Burnt sienna. 
Vandyke brown. 
Bone brown. 
Black lead, 
Blue black. 
Ivory black. 



Class II. — Moderately Permanent 



Flake white. 
Chrome yellow. 
Naples yellow (imi- 
tative). 
Kings' yellow. 



I Indian yellow. 
Green cinnabar. 
Emerald green. 
Malachite. 
Rose doree. 



Leitch's blue. 
Prussian blue. 
Antwerp blue. 
Asphaltura. 
Brown pink. 



TABLES OF PIGMENTS 289 



Class III.— Fugitive 



Citron yellow Burnt carmine. j Green lake. 

(ZnCr04). Crimson lake. Sap green. 

Yellow lake. Indian lake. Verdigris. 

Gamboge. Purple lake. Indigo. 

Primrose yellow. Violet carmine. Italian pink. 

Carmine. I 



19 



CHAPTER XXII 

SELECTED AND RESTRICTED PALETTES 

It is by no means easy to construct a palette which shall 
be at once artistically and scientifically perfect. For it 
is impossible to exclude every pigment which is suscep- 
tible of change, and it is unwise to include every pigment 
for which the fancies and partialities of particular painters 
desire to find a place. An artist discovers how to obtain 
a required hue by means of a special pigment, and is 
naturally reluctant to learn by tedious experimenting 
whether it cannot be secured by means of a more complex 
commingling of the ordinary paints. And although some 
great masters have done marvellous things with five, four, 
or even three pigments only, there is no sound argument 
which can be urged in favour of so severe a restriction. 
If much mixing of paints be bad, then a reasonable en- 
largement of the palette will render such mixing unneces- 
sary. And the artist wants something more than a mere 
match in hue : he knows that there is a peculiar quality 
of colour to be sought as well. He can make a trans- 
parent pigment opaque, but the reverse operation is im- 
practicable. Scumbling of one opaque colour thinly over 
another which is also opaque very imperfectly attains the 
effect of translucency. So the artist demands, in addition 
to a chromatic series of opaque pigments, a second series 

290 



SELECTED PALETTES 291 

possessed of transparency, or, at least, of translucency. 
Thus he adds to his cadmium yellow, aureolin ; to his 
vermilion, madder carmine ; to his emerald green, virid- 
ian; to his coeruleum or cobalt, ultramarine. And, 
moreover, he has to take account of the peculiar and 
often unexpected effects produced by the lightening of 
the tone of a pigment by commixture with white, and by 
the darkening due to the addition of black. Two nearly 
identical translucent reds may yield with white two dif- 
ferent hues, one verging on salmon, the other on rose. 
Charcoal-black yields with aureolin or Indian yellow a 
series of greens quite distinct from those obtained by 
mixing these yellow pigments with ivory-black. So the 
artist in making his first choice from the whole number 
of trustworthy pigments at his command, will proceed 
towards his final selection by two stages. He first re- 
tains those pigments which commend themselves to his 
judgment for their own chromatic qualities when un- 
mixed ; he then proceeds to test the characteristics of 
the remainder by trying the tints which they severally 
produce with white, the shades they yield with black, 
and the mixed hues to which they give rise by commix- 
ture with one another in twos and threes. To this set of 
experiments he adds another, in which these pigments 
are mixed, after the same manner, with those belonging 
to the first series. As the result of these trials the artist 
will be enabled to exclude several paints which would 
merely serve to encumber his palette. 

Before deciding finally as to the elements which shall 
be retained for our fundamental palette, it will be in- 
structive to study the selections of pigments which from 
time to time have been employed by artists of recent 
times and of the present day. The obvious weakness of 



292 



SELECTED PALETTES 



many of such palettes lies in their inclusion of a few 
treacherous pigments, such as asphaltum, and of a few 
evanescent pigments, such as carmine, crimson lake, and 
the bituminous variety of Vandyke brown. Nevertheless, 
in making our selection of pigments from the classified 
list previously given, we may obtain many useful hints 
from the palettes employed by artists with whose works 
we are familiar. It is particularly interesting to observe 
how extremely restricted were the sets of pigments used 
by several painters who are distinguished for the refine- 
ment and for the rich variety of hues shown in their 
works. In the following paragraphs the names of all 
decidedly fugitive and alterable pigments are printed in 
italics. 

Sir Joshua Reynolds, although too fond of varying his 
practice by the introduction of many dangerous com- 
pounds, and by the use, in the same picture, of incom- 
patible media and methods, executed many works between 
the years 1770 and 1775 with one or other of these five 
restricted palettes, containing from four to eight pig- 
ments : 



i. Flake white. 


Yellow ochre. 


Lake. 


Ultramarine. 


Black. 


ii. Flake white. 


Yellow ochre. 
Orpitnent. 


Lake. 
Caroline. 


Ultramarine. 


Black. 
Blue black. 


iii. Flake white. 


Yellow ochre. 
Naples yellow. 


Cartnine. 
Vermilion. 


Ultramarine. 


Black. 


iv. Flake white. 


AspJialttcin. 


Vermilion. 


Blue. 




V. Flake white. 


Naples yellow. 


Lake. 
Miniujii. 


Asphaltum. 





Paul Delaroche and H. Vernet employed these eleven 
pigments : 



Flake white. Yellow ochre. 
Naples yellow. 
Raw sienna. 



Vermilion. 
Lake. 

Brun rouge. 
Burnt sienna. 



Artificial ultra- 



Blue black. 
Ivory black. 



SELECTED PALETTES 



293 



W, Etty, R.A., used twelve pigments : 



Flake white. Naples yellow. 
Yellow ochre. 



Vermilion. 
Light red. 
Indian red. 
Lake. 



Terre verte. 
Blue verditer. 



Raw umber. 
Burnt umber. 
Black. 



Samuel Palmer employed in oil painting the following 
pigments, twenty-eight in all : 

Flake white. Naples yellow. Field's vermilion. Ultramarine. Vine black. 

Yellow ochre. Vermilion. Ultramarine Ivory black. 

Raw sienna. Light red. ash. Broivn madder. 

Cadmium i, 2, 3. Venetian red. Cobalt. Raw umber. 

Aureolin. ' Indian red. Antwerp blue. Burnt sienna. 

Madder carmine. Terre verte.^ 

Pink madder. Green oxide 
Rose madder. chromium. 

Emerald green. 

Thomas Wright J of Derby, employed fourteen pigments, 
and, it is to be presumed, flake-white also : 



Naples yellow. 


Vermilion. 


Carmine. 


Terraceum blue. 


Ivory 


Brown pink. 


Burnt ochre. 


Lake. 


Ultramarine. 


black. 




Indian red. 


Burnt lake. 


Prussian blue. 






Light red. 




Lake azure (?). 





From the Portfolio of 1875-6 we obtain the particulars 
given below concerning the pigments used by several 
well-known artists : the palettes quoted have been chosen 
as representative of different types. 

P. H. Calderon, R.A., employed fifteen pigments : 

Flake white. Naples yellow. Vermilion. Cobalt blue. Burnt sienna. 

Yellow ochre. Venetian red. Antwerp blue. Raw umber. 

Cadmium yellow. Pink madder. Vandyke brown. 

Raw sienna. Ivory black. 

Mars yellow. 

W. C. T. Dobson, R.A., ten pigments : 

Flake white. Yellow ochre. Vermilion. Cobalt blue. Raw umber. 

Raw sienna. Rose madder. Vandyke brown. 

Purple lake. Ivory black. 

The following are water-colour palettes : 
Alfred W. Hunt, seventeen pigments, and in addition 
Chinese white : 



Lemon yellow. Vertnilion. 

Gamboge. Light red. 

Yellow ochre. Indian red. 

Raw sienna. Madder lake. 



Terre verte. 



Cobalt. 
Ultramarine. 
Ultramarine ash. 
Smalt. 



Madder brown. 
Raw umber. 
Burnt sienna. 
Burnt umber. 



294 



SELECTED PALETTES 



Sir John Gilbert, R.A., fifteen pigments : 



Chinese white. Yellow ochre. 
Raw sienna. 



Vermilion, 
Light red. 
Venetian red. 
Indian lake. 



Cobalt. 

Artificial ultra- 
marine. 
Indigo. 
Prussian blue. 
Antwerp blue. 



Burnt sienna. 
Vandyke brown. 
Ivory black. 



The selection of a good set of permanent or fairly per- 
manent pigments must depend to some extent upon the 
idiosyncrasy of the artist, upon his training and methods 
of work, upon the class of subjects with which he deals. 
As a good general working set for oils, the following selec- 
tion is offered. It is arranged in two sections, the second 
including what may be called * supplementary ' pigments : 



c^„^: T r Flake white. 

;n.l H.I' J Cadmium yellow. 

. ^'^Z. 1 Aureolin. 

12 pigments, (^y^u^^ ^^^^^^ 

/"Raw sienna. 
Section II. I Naples yellow, 
includes -! Baryta yellow. 
12 pigments. I 



Vermilion. 
Madder car- 
mine. 
Light red. 

Purple madder. 
Madder brown. 
Cobalt violet. 



Viridian. 
Artificial ul- 
tramarine. 

Green oxide 
chromium. 

Terre verte. 

Cobalt green, 
light. 



Raw umber, 
Cappagh brown. 
Ivory black. 

Cobalt. 
Prussian blue 

(insol.). 
Burnt sienna. 



Emerald green is excluded, since it cannot be safely 
associated with cadmium yellow, but there is no reason 
why several more pigments should not be added in Sec- 
tion II., other than the desirability of limiting the number 
of paints to those really required. Garance doree, Rubens' 
madder, deep cobalt-green, burnt umber, Verona brown, 
vine black, and graphite might be added to the hst. On 
the other hand, further restrictions become by practice 
possible. One does not know what white, vermilion, 
yellow, and vine or charcoal black can do until one has 
purposely debarred one's self from the employment of 
any other coloured pigments. Here are two such re- 
stricted palettes : 

I. Flake-white, yellow ochre, light red, cobalt, ivory- 
black. 



RESTRICTED PALETTES 295 

2. Flake-white, cadmium yellow, vermilion, ultra- 
marine, ivory-black. 

A third restricted palette, containing ten pigments 
instead of five, is thus constituted : 

3. Flake-white, yellow ochre, cadmium yellow, aureolin, 
vermilion, madder carmine, ultramarine, viridian, Cap- 
pagh brown, ivory-black. 

It is scarcely necessary to say that the capacity of No. i 
for representing the range of natural hues is extremely 
limited ; indeed, it is fitted only for ' dead colouring,' and 
for the ' first painting.' With No. 3, however, we can 
imitate with a near approach to exactness all the pigments 
excluded from this palette, and we may therefore regard 
it as practically complete. Some of the hues obtained by 
the mixtures which it is necessary to employ for this pur- 
pose will be a little less luminous than the originals, since 
these hues will have been produced by the increased ab- 
sorption of certain elements of the incident white light — 
they are consequently duller, or have more grey in them. 
This palette. No. 3, is nearly the same as one devised by 
the late Mr. P. G. Hamerton (Portfolio, 1876, p. 132), which 
was constituted of flake-white, pale cadmium, yellow 
ochre, vermilion, rose madder, artificial ultramarine, 
emerald oxide of chromium, Vandyke brown, black. I 
have added one pigment, aureolin, and have substituted 
for pale cadmium, full cadmium yellow ; for rose madder, 
the more stable madder carmine ; and for Vandyke brown, 
Cappagh brown. Mr. Hamerton tested the range of his 
restricted palette by imitating with its constituents many 
of the excluded pigments. I give some of his results, as 
modified by my own experiments with my palette No. 3. 

Naples Yellow. — Imitated by flake-white, with cadmium 
yellow and a trace of yellow ochre : exact. 



296 RESTRICTED PALETTES 

Lemon Yellow. — Flake-white, cadmium yellow, with a 
trace of viridian : less brilliant than the original. 

Cadmium Orange. — Cadmium yellow, with vermilion • 
less brilliant. 

Light Red. — Vermilion, yellow ochre, Cappagh brown. 

Venetian Red. — Vermilion, yellow ochre, madder car- 
mine, a little Cappagh brown : exact. 

Indian Red. — Vermilion, trace of yellow ochre, madder 
carmine, ivory black : a good match, but less translucent. 

Cobalt Blue. — Artificial ultramarine, flake- white, a little 
viridian : less translucent ; does not match cobalt blue by 
artificial light. 

Prussian Blue. — Ultramarine, black, a trace of viridian : 
lacks the translucency and depth of the original. 

Raw Sienna. — Yellow ochre, aureolin, Cappagh brown. 

Burnt Sienna. — Madder carmine and Cappagh brown, 
with a trace of vermilion : less translucent. 

Emerald Green. — White, cadmium yellow, viridian, 
artificial ultramarine : not so brilliant as the original. 

Malachite. — White, cadmium yellow, yellow ochre, 
viridian, ultramarine. 

Terve Verte. — White, aureolin, viridian, ivory-black. 

Cobalt Green. — Ultramarine, viridian, trace of flake- 
white. 

Indigo. — Ultramarine, with black and trace of viridian : 
very close. 

Vandyke Brown. — Cappagh brown, with much madder 
carmine and a little ivory-black. 

It is needless to multiply further our illustrations of the 
resources at the command of the painter who limits him- 
self to our restricted palette of ten pigments (No. 3, 
page 295), as experimental trials of its capacity are 
easily made. 



RESTRICTED PALETTES 297 

So far, then, as regards selected and restricted palettes 
of oil colours. Some modifications must be made in our 
list in order to devise corresponding palettes of useful 
and enduring water-colours. In the more extended list 
(p. 294), zinc-white must replace flake-white, while 
vermilion, purple madder, brown madder, and cobalt 
violet must be discarded. In the limited palette (No. 3), 
the changes to be made comprise the substitution of 
zinc-white ( = Chinese white) for flake- white, the replace- 
ment of vermilion by one of the brightest native varieties 
of iron reds (the mineral turgite is perhaps the best kind), 
Cappagh brown by Mars brown, and of ivory-black by 
Indian ink. The two palettes (A. and B.) will then 
finally assume the following forms for water-colours : 

(A.) ( Zinc white. Light red. Viridian. Raw umber. 

Section I. J Cadmium yellow. Indian red. Artificial ultra- Burnt sienna, 

includes | Aureolin. iNIadder car- marine. Indian ink. 

13 pigments. \ Yellow ochre. mine. Cobalt. 

Section II. ) Raw sienna. Red ochre. Prussian blue Mars brown, 

includes V (insol.). Ivory black. 

5 pigments. J 

Doubtless artists will especially miss from this palette 
six pigments, namely, gamboge, vermilion, rose madder, 
brown madder, Vandyke brown, and indigo. But after 
the overwhelming evidence adduced in Chapter XXVI. as 
to the want of permanence shown by these water-colour 
paints, one feels compelled to exclude them. Our second 
and more restricted palette (B.) is thus composed : 

(B.) Chinese Yellow ochre. Red ochre. Ultramarine, Mars brown, 

white. Cadmium orange. Madder car- Viridian. Indian ink. 

Aureolin. mine. 

Although it is obvious that with these limited palettes 
it is impossible to produce exact imitations of every ex- 
cluded pigment, yet there are two considerations which 
must not be forgotten in estimating the influence of this 



298 RESTRICTED PALETTES 

defect on artistic painting. Foremost may be placed the 
fact that pigments are rarely employed wholly unmodified 
by admixture with others ; then it must be noted that the 
differences between our imitations and the original pig- 
ments which they are intended to replace are rather those 
of lessened brightness, translucency, and depth than those 
of hue. 



PART IV 
METHODS AND RESULTS 

Chapter XXIII.— Painting Methods. Chapter XXIV.— Study of 
Old Paintings and Drawings. Chapter XXV. — Conservation 
of Pictures. Chapter XXVI.— Trials of Pigments. 



CHAPTER XXIII 



PAINTING-METHODS 



As the grounds, vehicles, and pigments employed in 
painting have been already described in Parts I., II., 
and III. of this volume, it will not be necessary to do 
more in the present chapter than give a summary or 
general view of the chemistry of each method of employ- 
ing these materials. 

These methods are six in number, and may be thus 
defined : 



Methods 

1. Tempera 

2. Fresco 

3. Stereochromv - 

4. Oil - Painting) 

AND Spirit- v 
Fresco ) 

5. Water-Colour - 

6. Pastel, \ 
Charcoal, I_ 
Plumbago, j' 
Silver-Point ' 



Vehicles 

Egg-yolk emulsion ; solution of gelatin 
or albumen 

Lime-water, in both buon' fresco and 
fresco secco 

Aqueous solutions of alkaline silicates - 



Oil, and solutions of resin, wax, paraffin 

Aqueous solutions of gum, glycerin, 
honey ...... 



None 



Changes 

during Fixing 
j Desiccation or 
\ coagulation. 

Carbonation. 
Formation of in- 
soluble silicates. 
{Oxidation, 
Resinification, 
Evaporation, 
Solidification. 

Desiccation. 
None. 



I. Tempera-painting, or painting in distemper, is gener- 
ally assumed to include two, if not three, methods of 
procedure, in which different vehicles or media are em- 
ployed. These vehicles all contain a nitrogenous con- 
stituent ; but in one of them — and that the most important 

301 



302 TEMPERA -PA INTING 

— oil or fat is present in addition. Tempera-grounds 
must be rigid, tenacious, and firm; they need not be dry, 
but if organic pigments are to be used, they should not 
contain caustic lime. Thus, a surface of plaster made 
with slaked lime and sand must have been so long 
exposed to the air as to have absorbed the amount of 
carbonic acid necessary to convert the hydrate of lime 
present into ' mild lime ' — that is, the carbonate. To 
detect the existence of caustic lime in such a painting- 
ground recourse may be had to test-papers. Three kinds 
are available for this purpose. Thus, yellow turmeric-paper, 
first wetted and laid upon the surface of the plaster, 
should show no change of colour ; if it become reddish, 
the presence of caustic lime is indicated. Under the 
same circumstances red litmus-paper turns blue or purple, 
while phenolphthalein-paper acquires a crimson hue. If 
these tests show the absence of caustic lime, the painting 
may be commenced, otherwise the surface must be car- 
bonated by syringing it or washing it with water charged 
with carbonic acid gas. These precautions are, of course^ 
unnecessary in cases where the painting-ground has been 
prepared with plaster -of- Paris or other neutral com- 
positions of which caustic lime is not a component. 
Before commencing work the painting-ground must be 
slightly and uniformly moistened with distilled water, 
and then coated with weak size. The pigments to be 
employed are those recommended for use as water- 
colours; they are thoroughly mixed with the medium 
to be employed, namely, egg-yolk emulsion, or size, or 
prepared white of e^g. These media serve not only to 
bind the pigments to the ground, but also the coloured 
particles to one another. To render the egg-yolk more 
tractable, its alkaline reaction should be exactly neutral- 



TEMPERA -PA INTING 303 

ized by the cautious addition of a very few drops of white 
vinegar — fig-tree sap or white wine was sometimes 
formerly employed for the same purpose. Some artists 
content themselves with diluting the egg-yolks with a 
little water, others add a small proportion of white of egg, 
previously shaken with a little water and filtered. To 
keep the egg-emulsion sweet, a lump of camphor or a 
few cloves may be put into it. Size and also white of 
egg have been employed in tempera-painting. The white 
of egg needs dilution with water, thorough shaking, and 
then filtering through muslin. When egg-yolk is used 
in this method of painting, the oil in it gradually hardens, 
while the albuminoid matters which accompany it be- 
come partly insoluble and coagulated. As the amount 
of oil in egg-yolk is twice as great (31 per cent.) as the 
albuminoid matters (15 per cent.), this vehicle presents 
considerable resemblance to those employed in oil- 
painting, the albuminoid matters corresponding in a 
measure to the resins often used in the latter method. 
This vehicle does not act so effectually as oil and varnish 
in ' locking up ' pigments, and so the protection against 
change which it affords is less. Moreover, instances have 
been observed in which the sulphur present in the albu- 
minoids of egg-yolk has acted injuriously upon some of 
the pigments of the picture ; but by excluding, as we 
now do, all paints containing lead and copper from the 
tempera-palette, accidents of this kind are prevented. A 
finished tempera-picture was often — one might almost 
say generally — rubbed with a cloth and then varnished, 
the varnish being often made by dissolving sandarac in 
oil. The tone of the colours was thus warmed, while 
further protection was at the same time afforded against 
moisture and impure air. 



304 FRESCO-PAINTING 

2. In fresco-painting — both buon' fresco and fresco secco 
— the ground must not only be wet, but caustic. In true 
fresco the pigments are appHed to the last and freshly- 
spread coat of plaster before it has had time to absorb 
more than a trace of carbonic acid from the air; the 
painting-ground is in fact saturated with an aqueous 
solution of hydrate of lime, while there remains a large 
reserve of this compound in an undissolved condition. 
When on such a surface a layer of pigment mixed with 
water is placed, as that water evaporates the lime-water 
in the ground diffuses into the paint, soaks it through 
and through, and gradually takes up carbolic acid from 
the air, thus producing carbonate of lime, which acts as 
the binding material in this method. As there still exists 
an ample reserve of hydrate of lime in the ground, wetting 
the painted surface with pure water will cause more of 
this hydrate to enter into solution, and so the liquid 
present in the plaster will be reinforced with a fresh 
supply of the binding material. Ultimately the ground 
and the pigment become incorporated and harden together. 
If more binding material be required, it may be intro- 
duced by means of lime-water itself, or even by baryta- 
water, which contains about twenty times as much 
hydrate of baryta as the strongest lime-water contains of 
hydrate of lime ; these liquids or hydrate of lime may 
also be mixed with the pigments used. Although the 
chief binding material in fresco-painting is this carbonate 
of lime, yet with some plasters and with some pigments 
another substance is produced. This is silicate of lime, 
produced by the action of caustic-lime in solution upon 
the soluble silica of the plaster or of the pigments. 
Some sands, infusorial earths, and ochreous pigments, 
contain such soluble silica, but it is certainly not present 



FRESCO-PAINTING 305 

in every case. Silicate of lime as a binding material is 
more permanent than the carbonate. 

In fresco secco the plaster is allowed to harden, and, in 
some measure, to dry, and the operation of painting may 
be continued at leisure. The ground immediately before 
beginning work is moistened with lime- or baryta-water, 
and the pigments are mixed with one or other of these 
liquids, or with a little slaked lime. This modified pro- 
cess is far easier of execution than true fresco ; but the 
fixation of the pigments, though resulting from the same 
cause, is less complete. 

In the treatises of Cennini and other later writers the 
expression ' painting in secco ' is generally employed to 
designate any process of tempera-painting, but the fresco 
secco described in the preceding paragraph was practised 
before and during the thirteenth century as the precursor 
of buon' fresco, and is briefly mentioned in Theophilus 
('Schedula,' Book I., chapter xv.). 

The protection afforded to the pigments by the binding 
material in fresco-painting is not generally very efficient. 
In the case of a dry wall, free from soluble saline matter, 
and exposed to a pure atmosphere, it may remain good 
for centuries. But in air contaminated with the products 
of the combustion of coal and gas, and with tarry and 
sooty impurities, a fresco picture soon perishes. The 
binding carbonate of Ume is converted into the sulphate, 
breaking up the paint, and becoming itself disintegrated 
in the process of change. Through the same cause, and 
through the production of sulphate of magnesia from the 
carbonate of magnesia in the plaster, even the layer of 
paint itself may scale off, while the lodgment of dirt and 
soot upon the surface obscures such colours as still remain 
in their place. And fresco-paintings often show scaling- 



3o6 FRESCO-PAINTING 

off, by reason of the interposition of a film of carbonate 
of lime between the coats of paint — a. film formed during 
the completion of the picture. 

True fresco did not come into use in mediaeval times 
until the close of the fourteenth century. About the year 
1390, Pietro d'Orvieto painted some subjects from Genesis 
in the Campo Santo at Pisa. In 1503, Pinturicchio, at 
Siena, began some works in fresco, which he finished in 
tempera with lakes and other pigments injured by lime. 
This mixed method was much used in Italy to a late 
period, as it enabled a greater richness of effect to be 
attained. For the palette of the painter in true fresco is 
severely restricted in certain directions, very few colours 
of organic origin withstanding the decomposing action of 
lime. It is a good plan to test each pigment intended to 
be employed in this method : The pure pigment is thinly 
painted over a slab of plaster-of-Paris, and then half of it 
is to be moistened with lime- or baryta-water. No change 
of hue, only a lightening of the tone, should be observed, 
after drying, in the treated portion. Prussian blue may 
be named amongst the pigments most quickly and seriously 
altered by lime ; it becomes a mere stain of rust. 

Although it might have been expected that the earthy 
pigments, terre verte, yellow ochre, and raw sienna, would 
prove peculiarly suitable for use in fresco-painting, the 
examination of works executed in this method, during 
the last half-century in England, does not confirm this 
expectation. Indeed, it is found that the most friable 
portions of such frescoes are precisely those in which 
these pigments have been freely employed. This remark 
applies particularly to terre verte, which is found to have 
become swollen and easily detachable. 

As lime in the caustic state acts strongly upon wood. 



FRESCO-PA INT IN G 307 

it is necessary to employ palettes of zinc or glazed 
earthenware ; bone or ivory palette-knives are preferable 
to those of steel. 

Asiatic Fresco. — The remarkably successful explorations 
of Sir Aurel Stein among the buried sites of Chinese 
Turkestan have brought to light numerous examples of 
a peculiar variety of fresco-painting. In the brief ' Guide 
to the Stein Exhibition of 1914,' in the British Museum, 
the method is vaguely described thus : * A preparation of 
lime is spread over a foundation of mud and chopped 
straw, and the pigments applied to the surface while it 
is wet' In reality the process adopted in these works, 
dating from the third to the tenth century of our era, may 
be more exactly described in the following words : On 
a backing of the ordinary local loess mixed with the 
chopped stems and leaves of the common reed, there 
was spread a thin flat coating of impure burnt gypsum 
made into a cream with water. Pigments such as an 
iron red, malachite, a charcoal grey and an ochre, some- 
times mixed with the cream of burnt gypsum, were then 
painted on while the surface was still moist. On drying 
the colours became fixed, not by carbonation, as in true 
fresco work, but simply by loss of the solvent water 
present and the crystallization of its content of gypsum. 
As I made numerous analyses for Sir Aurel Stein of 
painted plaster, from sites at Kadalik, Miran, and Mingoi, 
I can speak with confidence of the essential distinction 
between Asiatic and European fresco : the former is 
essentially a plaster-of-Paris method. 

3. In stereochromy, or water-glass painting, a process 
introduced more than sixty years ago, the fixative em- 
ployed is an alkaline silicate dissolved in water. From 
time to time different experimenters have improved the 



3o8 STEREOCHROMY 

painting-grounds, the preparation of the pigments, and 
the mode of applying the fixing liquid ; but the main 
chemical actions involved in this method of painting are 
identical in all the modifications which have been intro- 
duced. The constituents and preparation of painting- 
grounds adapted for this process have been discussed in 
Chapter II. The pigments should be treated, as recom- 
mended by Kuhlmann, with some of the fixing liquid, 
and then reground ; in some cases they require the previous 
addition of oxide of zinc, powdered marble, powdered glass, 
carbonate of baryta, soluble silica, hydrate of alumina, etc., 
in order that their natural inaptitude for equal fixation by 
the alkaline silicate should be remedied. Opinions differ 
as to the desirability of treating the painting-ground with 
some of the water-glass solution before laying on the 
colours ; but it is essential that if a solution of this silicate 
be used at this stage, it should be very dilute. The finished 
painting is sprayed with a warm dilute solution of potash 
water-glass or potash-soda water-glass, to which has been 
added liquor ammoniae. The surface is shortly afterwards 
washed repeatedly with hot distilled water ; and, if neces- 
sary, the application of the water-glass solution, and the 
subsequent washing, are repeated. The final result of 
these operations is to bind the particles of pigment to 
one another, and to the ground, by means of an insoluble 
double silicate. This silicate, formed partly out of some 
of the constituents of the ground, of the pigments, and of 
the water-glass, mainly consists of silica, lime, and potash ; 
it often contains zinc, magnesia, and alumina. The soluble 
salts removed by washing the painting with water are the 
carbonates of potash and ammonia ; when, however, soda 
is present in the water-glass, carbonate of soda has been 
formed, and is removed at the same time. The pigments 



OIL-PA INTING 



309 



employed in stereochromy are more limited in number 
even than those available in fresco-painting, and consist 
chiefly of natural oxides and earths, the artificial oxides 
and hydrates of chromium and iron, cobalt green, ultra- 
marine, cobalt blue, and ivory-black. 

4. Oil-Painting and Spirit-Fresco. — The essential charac- 
teristic of these methods is to be found in the use of a 
binding material which is in itself insoluble in water. 
The painting-ground employed should be dry, and free 
from alkali and from soluble salts. If it be primed 
canvas or panel, it is a good plan to cleanse it with oxgall 
and water, or with a very weak solution of carbonate of 
ammonia, before commencing work. A discoloured lead- 
priming should be restored to its original brightness by 
laying a sheet of white blotting-paper upon it, and then 
just saturating this paper with a solution of peroxide of 
hydrogen. The moist surface is now exposed to a 
moderate degree of heat — as by holding it in front of a 
fire — which greatly quickens the activity of the peroxide. 
When the paper has become dry, it may be removed, and 
the bleaching of the tarnished ground will be found to 
have been effected, the brown sulphide of lead having 
been oxidized into the white sulphate. In order to learn 
whether a plaster-ground or a wall is sufficiently dry to 
be safely painted upon in oil or spirit-fresco, the gelatin- 
test may be employed, A small oblong piece of coloured 
sheet-gelatin is held firmly and closely against the plaster 
or wall, by means of a stick applied at the centre. If 
hygroscopic equilibrium have been established between 
the wall and the air, the gelatin will remain flat ; if the 
wall be moister than the air, the sheet will curl outwards, 
the inner surface becoming highly convex. Slate and 
several other suitable painting-grounds may be dried and 



310 OIL-PAINTING 

further prepared for work in oil or spirit-fresco by heating 
them gradually in a water-oven up to the temperature of 
boiling water, and then rubbing them with a piece of 
hard paraffin-wax. The slate is again heated in the water- 
oven, withdrawn, and then at once rubbed with a dry, 
warm cloth, so as to remove all excess of paraffin wax. 
Other methods of treating stone, etc., for the reception of 
oil-colours have been previously given. A very con- 
venient means of neutralizing the residual alkalinity of a 
lime-plaster ground intended for oil or spirit-fresco painting 
is afforded by linoleic acid.* This liquid fatty acid is an 
article of commerce, moderate in price, and easily obtain- 
able. A wide-mouth tin of it is placed in a vessel of 
boiling water ; when the linoleic acid is hot, it is paid on 
to the surface of the plaster with a wide brush, any excess 
being removed by wiping the ground with a cloth. Solid 
stearic acid may be melted and used in the same way, 
but its effect is inferior. 

The vehicles employed in these methods of painting are 
not miscible with water— are, in fact, hydro fuge materials 
repellent of moisture. If an absorbent ground or other 
porous material be soaked with water, and then covered 
with oil, as the water evaporates the oil penetrates, and 
at last completely takes its place. But, on the other 
hand, the reverse process cannot be carried out, since the 
water outside will not displace the oil inside. These 
vehicles are either oils or else solid substances in solution 
— solids which, though insoluble in water, may be dis- 
solved with more or less ease in one or other of a long 
series of liquid solvents (Chapters V., VI., XI., and XII.). 
The changes experienced by these vehicles and their 

* By linoleic acid is here meant the mixture of fatty acids 
obtainable from raw linseed oil. 



OIL-PAINTING 311 

constituents during the painting process may be thus 
summarized : 

(a) The oils used absorb oxygen from the air, increasing 
in weight thereby to the extent of 10 or 11 per cent. — 
such increase in weight being accompanied by a consider- 
able increase in bulk. This latter change is clearly shown 
when a layer of a drying oil, spread upcn glass, is allowed 
to dry ; it then becomes rippled or wrinkled from ex- 
pansion ; such expansion, owing to the viscosity of the 
oil, takes place mainly in a direction perpendicular to 
that of the surface of the glass. 

(h) The above-described absorption of oxygen by the oil 
employed in painting results in the formation of a sub- 
stance or mixture of substances called linoxme. Now this 
product is not only solid instead of liquid, but it is almost 
insoluble in the usual solvents of oils unlike the oil from 
which it has been formed. But there are circumstances, 
not yet accurately defined, in which linoxine itself occa- 
sionally suffers a peculiar change, finally becoming brown 
in colour, tacky in consistence, and soluble even in spirits 
of wine. This degradation of linoxine is, however, of very 
rare occurrence in the ordinary practice of oil-painting. 
A singular circumstance connected with the transformation 
of ' linolein ' into ' linoxine ' has been noticed ; this change 
is accompanied by the formation of hydrogen peroxide, a 
compound which is also produced during the oxidation of 
the terpenes. The continuous production of the peroxide 
may be recognised on the surface of an oil-painting long 
after it has been completed by the blue colour which it 
develops in starch-paste containing potassium iodide. 

(c) The resins present in varnishes and media contract 
for some time after the major part of their volatile solvent 
has escaped by evaporation, and thus leave a residue which 



312 OIL-PAINTING 

becomes fissured. In a properly-proportioned medium 
this contraction should be balanced, or rather more than 
balanced, by the expansion of the oil present. Hence the 
desirability of associating a varnish (or a resin dissolved 
in a volatile solvent) with a drying oil, in this method of 
painting. 

(d) Waxes and solid paraffins, when once deposited from 
a solution by the escape of the solvent, neither expand 
nor contract by desiccation or oxidation, but only through 
changes of temperature. 

(e) Most of the liquid solvents simply evaporate, leaving 
no fixed residue due to their previous presence. But spirit 
of turpentine and oil of spike generally behave differently. 
Some kinds of spirit of turpentine differ from the majority 
in this particular, but the remainder suffer two simul- 
taneous changes. A portion evaporates ; another portion 
absorbs oxygen from the air, becoming converted into a 
sticky, yellow, and resinous substance, which remains 
behind. The resin thus formed is a very objectionable 
constituent in the structure of a picture, and its production 
should be avoided either by employing a variety of tur- 
pentine not subject to easy resinification, or by using a 
freshly-distilled turpentine which has been secluded from 
the air, and in which a few lumps of freshly-burnt lime 
have been placed, to remove water and such resinous 
matters as may be produced. 

An important precaution to be observed in the 'conduct ' 
of a painting during its progress is based upon the two 
actions just referred to, namely, the oxidation of the oil 
during its hardening, and the escape of volatile solvents. 
The latter action takes place more easily than the former, 
and so if a picture is to be carried on rapidly to comple- 
tion, the earlier and lower paintings should contain less 



OIL-PAINTING 313 

oil than those nearer the surface, into which more oil and 
less resin (copal or amber), dissolved in some volatile 
solvent, should be introduced. If the reverse order be 
followed, the highly oleaginous layers below, having had 
no sufficient opportunity for oxidizing, drying, and harden- 
ing, v-/ill be rent by the strong and quickly-drying resinous 
layers above them. 

The harder resins, paraffin-wax, wax, and oil, possess 
in varying degrees the power of ' locking-up ' the pigments 
with which they are mingled, in such a way that these 
become much less liable to act upon one another, and to 
suffer injury from external agencies. In a measure they 
repel and exclude moisture and oxygen — two of the chief 
agents of chemical change. But the value of these 
' locking-up ' materials has been exaggerated : they often 
prove quite ineffectual in preventing the oxidation or 
other change suffered by non-permanent pigments and the 
inter-action of pigments. For instance, the oil which 
surrounds each particle of cadmium yellow and emerald 
green, in a mixture of these two oil-paints, is not capable 
of preventing the formation of the black sulphide of 
copper. And Dr. A. P. Laurie has found that when a 
layer of linseed-oil is interposed between these oil-colours 
separately spread, it is the emerald green which appears 
to travel towards the cadmium yellow — perhaps owing to 
its solubility in the medium. In consequence, the pro- 
duction of spots of black sulphide of copper occurs chiefly, 
if not entirely, on that side of the oil-layer which is in 
contact with the cadmium yellow. To Dr. Laurie we are 
also indebted for a very ingenious method of comparing 
the locking-up function of various oils and resins. Dr. 
Laurie prepared some anhydrous sulphate of copper which 
is white, but acquires a blue colour when exposed to 



314 OIL-PAINTING 

moisture. He ground this white sulphate with various 
media, painted glass slides with the mixtures, dried them 
in a desiccator, and then exposed them to moist air. A 
solution of amber in turpentine proved superior, in its 
power of resisting the access of moisture, to boiled linseed- 
oil, oil-copal varnish, amber dissolved in oil, resin or 
mastic dissolved in turpentine. Another set of trials, in 
which the test substance was ground in linseed-oil, allowed 
to harden in a desiccator and then coated with different 
varnishes, indicated a temporary superiority on the part 
of mastic in turpentine, and of oil-copal varnish over 
amber or copal in turpentine. The inferiority of the latter 
solutions may be due to the rupture in continuity of the 
resinous films which they leave on evaporation. (See 
Journal of Chemical Industry, June, 1890.) But it must 
not be forgotten that many an old oil-picture furnishes 
distinct evidence of the value of resinous matters (such 
as Strasburg and Venice turpentine) in locking up such 
changeable and destructive pigments as verdigris and 
orpiment. The slow and laborious execution of such 
paintings constituted an important element in the success 
achieved, for each layer dried and hardened before the 
next was applied. 

It should be noted that different oil-paints contain very 
different percentages of oil. This fact should be taken 
into account, so far as possible, in adjusting the amount 
of resinous matter to be introduced during the course of 
work upon an oil-picture. A table giving approximately 
the quantities of oil required in grinding 100 parts of 
various dry pigments as oil-paints will be found on 
page 66. Further information concerning such pigments 
is given in Chapters XIII. to XIX. 

In completing an oil-picture, the three operations of 



OIL-PAINTING 315 

' glazing,' ' oiling out,' and * varnishing ' remain to be con- 
sidered. As to glazing and oiling out, it should be stated 
that drying oil, with a little copal or amber varnish, should 
alone be employed — mastic varnish should never be added 
to the oil. Of course oil-paints are used in admixture 
v^ith oil and copal for glazing purposes. If mastic be 
introduced, a risk is incurred of its partial removal during 
any cleaning operation to which the picture may be after- 
wards subjected. The question of the kind of varnish to be 
finally applied to an oil-picture has been much discussed. 
Our choice lies between a strong irremovable varnish, and 
a weak one capable of being abraded by friction, or of being 
dissolved by the application of a suitable solvent, which 
will not touch the true painting beneath. Mastic dissolved 
in turpentine fulfils the latter conditions ; copal or amber 
dissolved in oil and thinned with turpentine, and mixed with 
a Httle oil, constitutes a strong, hard, irremovable protec- 
tion to the surface, and becomes a part of the picture itself. 
Under no circumstances should any varnish be applied to 
the painting until the latter has become thoroughly hard 
and dry ; the danger of tearing the layers of paint by 
such application will then have been reduced to a mini- 
mum. A further advantage of delay in varnishing a picture 
accrues through the increasing insolubility with age of 
the oxidized oil present therein, the pigments associated 
therewith becoming less liable to removal by any treat- 
ment to which the work may afterwards be submitted. 

The chemistry of Gambier-Parry's spirit-fresco method, 
and of the process in which paraffin- wax and copal varnish 
are employed as the vehicle, is essentially the same as that 
of oil painting. The wax or paraffin-wax is introduced 
merely to secure a matt surface. Pictures executed in 
these methods are, of course, never varnished. The 



316 SPIRIT-FRESCO PAINTING 

method of spirit-fresco was devised by the late Mr. 
Gambier- Parry with the object of obtaining such effects 
in mural paintings as are realized in true fresco, but with 
greater ease in working, and greater permanence under 
adverse atmospheric conditions. He desired to exclude 
linseed or other fixed drying oils completely from the 
medium and other materials employed. With this end 
in view, he directed that the pigments used should be 
ground up, not with oil, but with the medium itself. He 
was apparently unaware that the copal varnish, which 
enters largely into the composition of his vehicle, contains 
a greater proportion of oil than of any other ingredient 
(see Chapter XII.). So, after all, the medium used in 
spirit-fresco differs from that generally employed in oil- 
painting rather in the proportions than in the nature of its 
ingredients. Thus in working with it we shall find that 
its binding character is obtained as a result of the same 
two changes which cause the fixing and solidification of an 
oil painting, namely, the oxidation of the oil, and the 
desiccation of the resin. The wax present suffers no 
chemical alteration at first, but merely solidifies, although 
after the lapse of years it is liable to produce a kind 
of exudation or bloom ; indeed, in the course of years the 
wax may wholly disappear. It should be added that the 
painting-ground for this method of working is first 
prepared with the medium diluted with oil of turpentine 
(see Chapter II.). 

The method of painting with the paraffin-copal medium 
involves the same chemical and physical changes as 
those which occur in the use of the spirit-fresco vehicle, 
and is carried out in the same manner. Colours stiffly 
ground in oil may be used or in a mixture of the medium 
with oil : dry colours ground in the medium generally 



WATER-COLOUR PAINTING 31? 

are to be preferred. The medium may be diluted to any 
desired consistency with spirit of turpentine or with oil 
of spike, but no dilution further than that required to 
secure perfect freedom in the manipulation and use of the 
paints is desirable, while it is important to remember that 
the use of abundance of medium is necessary to bind 
the particles of pigments firmly together. Artists have 
sometimes found that a picture painted in spirit-fresco 
will cede colour to a cloth used in rubbing its surface. 
This result is due either to excessive use of a diluent 
in working with this medium, or to a deficiency of oil 
in the copal-varnish used. I have never known a friable 
surface to be formed where the colours employed had 
been ground in oil instead of in the medium, or where 
a little extra oil had been added to the latter. 

5. Water -coloicr Painting. — The usual binding material 
in this method is gum ; glycerin and honey are also 
employed to some extent. Raw honey should never be 
used, but only one of the sugars it contains, known to 
chemists as Icevulose (Chapter VIII.). Great care must 
be taken not to introduce any unnecessary excess of 
either glycerin or laevulose, as these materials attract 
moisture from the air, and we know that moisture 
is one of the most potent agents in causing injury to 
works in water-colour. Glycerin and laevulose are, 
however, useful, when employed in moderation, for pre- 
serving the pigments in working condition, and in counter- 
acting the tendency of gum to crack. The media used 
in water-colour painting, consisting wholly of aqueous 
solutions, afford very slight protection to the pigments 
used. In the presence of the moisture of the ground 
(paper often contains naturally 10 per cent, of water) 
and of the air, water-colour pigments have abundant 



3i8 WATER-COLOUR PAINTING 

opportunities, not only of acting upon one another^ 
wherever from their chemical constitution such action 
is possible, but also of being acted upon by external 
agents. Thus it comes to pass that several pigments 
(vermilion, for instance, and emerald green) useful in 
oil-painting cannot be safely used as water-colours. 
Again, there are a few pigments (such as strontia yellow) 
which are soluble in water, and which consequently may 
gradually sink into the paper, and so partially disappear 
from the surface. 

Assuming the paper-ground to be of linen-pulp, and 
free from ' filling,' from bleaching substances, from anti- 
chlors, and from fragments of iron, it will still contain 
about 5 per cent, of size. When in preparation for 
painting it is moistened with water, this size swells, and 
on the subsequent application of washes of pigments, 
enters partially into mechanical union with them, so 
that the various coloured materials applied to the sur- 
face become associated with the size rather than with 
the paper-fibres. One paint, Indian ink, itself contains 
size, and for this reason when washes of it are laid upon 
paper previously damped, their incorporation with the 
size of the latter is so intimate that their removal is 
impracticable. The size in a water-colour drawing be- 
comes in time partly coagulated and insoluble ; the gum 
merely dries. Instances are known where the size has 
in some degree ultimately perished. 

6. Pastel, Charcoal, Plumbago, Silver-point. — The com- 
mon characteristic of all the processes which form our 
sixth group is the absence of any vehicle or binding 
material. The usual ground on which drawings in 
the above-named substances are executed is paper 
(Chapter I.); but as the hold of coloured chalks and 



PASTEL-PAINTING 3i9 

of charcoal is very precarious, the paper is generally 
mounted on some comparatively rigid backing, such as 
millboard, cardboard, copper, or panel. If a chalk or 
charcoal drawing be carried out on paper which has first 
received a wash of gum-water or of dextrin-solution, it 
is easy to effect a partial fixation of the powdery pigment 
by subsequently steaming the finished work, although it 
is usual to employ a fixing solution in the form of very 
fine spray to the finished drawing. For pastel work a 
specially prepared paper is now generally employed. 
This has a surface of finely-powdered pumice, which 
affords an efficient tooth, and helps in securing the 
coloured chalks or clays. This result is further aided 
by the plan of working in and mingling the pigments by 
means of rubbing with the fingers and the palm of the 
artist's hand. Pastel-paper is often made of inferior 
pulp, and lacks strength. It should be less sized than 
paper intended for water-colours. Pastel colours are 
generally made with a basis of purified chalk or pipe-clay 
mingled with the usual pigments in powder, a slight 
degree of cohesion being secured by makmg up the 
crayons with starch -paste or gum-tragacanth. 

H For fixing pastel-drawings it is convenient to use 
the following medium: Pound 15 grams dry casein and 
3 grams of borax together, and then shake the powder 
with constant stirring into 100 cubic centimetres of dis- 
tilled water. After some hours a syrupy mass will have 
been formed. Dilute this with more water so as to 
make the liquid up to 750 cubic centimetres; then add 
250 cubic centimetres of spirits of wine. After a time 
a white precipitate may form ; pour off the somewhat 
opalescent liquid from this sediment. This fixative is to 
be sprayed on to the face of the pastel, care being taken 



320 ■ PASTEL.PAINTING 

to prevent the liquid from gathering in actual drops upon 
any part of the drawing. When the surface looks moist 
and shiny, it shows that it has been sufficiently dosed 
with the fixative. The more completely the ground is 
protected by the colour laid on, the less risk there is of 
the fixation affecting the appearance of the picture. If, 
however, the effect of the work has been obtained by a 
mere whiff oi the powdery pigment, it is wiser to omit 
the fixing procedure, for the delicacy of such very fine 
layers of colour would thus be impaired. In any case, 
the artist who is concerned for the permanence of his 
work will always try to obtain his effects by building up 
as solid a layer of colour as possible. 

U Pastels, as already mentioned, containing no binding 
material, or next to none, drawings made with them are 
exempt from the drawbacks inseparable from the use of 
vehicles. Consequently there is no fear of the surface 
cracking, darkening, blooming, becoming brown, or other- 
wise altering. When we further consider that pastel- 
drawings, unlike water-colours, depend for their effect on 
the presence of a fairly solid layer of pigment, and that 
many colours which are unstable when employed in 
other methods of painting, have proved to be durable in 
pastel, we are bound to admit that this beautiful technique 
is not only simple in method but expressive in the effects 
which it commands ; but is only capable of producing 
drawings which last better than most others, provided 
they are protected by glass, and are not exposed to 
damp. 

H Since the pastel crayons of the shops bear usually no 
indication of the pigments employed to colour them, and 
frequently contain unstable coal-tar dyes, special care 
must be taken to test their permanence when exposed to 



PASTEL-PAINTING 321 

light. To do this it will suffice to expose to direct sun- 
shine in bright weather one half of a strip on which clear 
tones of the set of coloured pastels which we wish to use 
have been spread and fixed. It is possible, if the sun- 
shine be strong, to detect the more alterable pastels after 
a few days' exposure. For serious work the artist should 
use only such pastels as have stood the test. It is 
fortunate that, owing to the absence of any medium, 
chemical interaction between pastel -pigments when 
mixed together in the process of painting is virtually 
non-existent. 

Details concerning the making at home of pastel- 
crayons will be found in W. Ostwald's * Letters to a 
Painter,' English edition, pp. 22-27. Here we need add 
only the following memoranda : Excellent pastel-grounds 
may be prepared by laying, on Bristol board or stout 
drawing paper, a thin and even coat of powdered pumice 
mixed with liquefied starch (see p. 95). Or the same 
coat may be spread upon a surface of a fine fabric, such 
as thin calico, linen, or silk, previously secured to the 
board or paper by means of starch-paste. 

In plumbago (lead-pencil) and silver-point work, the 
mechanical adhesion of the coloured particles is naturally 
less imperfect than in pastel, a portion of the plumbago 
or silver becoming, in fact, incorporated with the fibres 
of the paper-ground. This is particularly the case with 
silver-point, in which method the ground receives a 
particular preliminary preparation. One of the best 
materials for this purpose is Chinese white (oxide of 
zinc). An even wash of this pigment in the form of 
* moist ' water-colour is first spread over the paper. As 
a silver-point drawing is often heightened with touches 
of Chinese white, it is desirable to bring these into promi- 



322 SILVER-POINT DRAWING 

nence by tinting the ground. For this purpose a small 
quantity of some permanent pigment is mixed with the 
wash of Chinese white. Yellow ochre, raw umber, green 
oxide of chromium, Mars violet, ultramarine with a little 
ivory-black, may be used. The ' tooth ' of surface which 
increases the attrition of the silver-point is, however, 
furnished by the presence of the Chinese white. It 
should be added that the silver used should be free from 
any alloy of copper, which hardens the metal, but may 
advantageously contain a few per cents, of metallic lead ; 
an alloy of 2 parts of lead with i part of tin was some- 
times used instead of silver. The silver in silver-point 
drawings is liable to become brown from the sulphur 
compounds in impure air. The blackening of the high 
lights in old silver-point drawings is due to the tarnishing 
of the lead white employed ; it may be got rid of by 
keeping the drawing for some time in an atmosphere of 
moist ozone, or by a careful treatment with a solution of 
hydrogen peroxide in ether. 

A pointed pencil of pure gold is occasionally used 
instead of one of silver or graphite. It produces on a 
prepared paper surface the same grey line, and is theo- 
retically a perfect material for drawing purposes. But, 
strange to relate, gold-point drawings have been observed 
to suffer change, becoming nearly invisible, not by reason 
of any chemical action on the metal, but in consequence 
of a rearrangement of the metallic particles whereby 
their grey hue disappears and the original yellow lustre 
of the gold is resumed. Drawings in platinum-point are 
not susceptible of this change. The platinum employed 
must be pure, otherwise this metal is too hard for com- 
fortable manipulation. 

Pastel or coloured chalk drawings frequently show a 



PA ST EL -PA INTING 



323 



higher degree of preservation, so far as certain hues are 
concerned, than contemporary works executed in oil. One 
can easily account for the pure and fresh air of old pastel 
drawings, knowing that they have been carefully mounted 
and framed, and that there has been no oil or resin to 
yellow and darken the pigments. But how can the remark- 
able state of preservation in which the ' carnations ' are 
found in so many examples be explained ? Has the 
intimate commixture of chalk or of clay with crimson lake 
preserved the latter from the destructive action brought 
about by light ? If there have been such a preservative 
action, has it been physical rather than chemical ? 
Answers to such questions must be reserved until the 
chemistry of coloured pastels has been thoroughly studied. 
It should, however, be recollected that the white basis of 
coloured pastels is not always the same. In the eighteenth 
century it seems to have been invariably purified chalk, 
that is, 'whitening' or 'whiting,' which is essentially 
calcium carbonate. But, on examining lately a well-known 
make of French pastels, a considerable percentage of 
calcium sulphate was recognised, in addition to chalk. 
Further experiments seem to show that the colouring 
matter used is first ground up with a mixture of chalk and 
plaster-of-Paris, and that, in consequence, the subsequent 
addition of water causes the whole to set into a mass of 
just sufficient tenacity to hold together, though very soft 
and fragile. In this way the use of starch-water as a 
binding material is obviated. In other pastels pipe-clay 
or china-clay has been employed as the basis for the 
colouring matter. 

Paintings and drawings executed in fresco, in tempera, 
and in water-colours, may be protected from the hostile 
attacks of impure air and moisture by applying to the 



324 PASTEL.PAINTING 

finished work a coating of pure hard paraffin-wax. If 
such an after-treatment is contemplated in the case of a 
work executed in water-colour the amount of vehicle em- 
ployed (gum, etc.) should be reduced to the necessary 
minimum. The mode of applying the paraffin-wax is 
described further on at the end of Chapter XXV., 
pages 356-357- 



CHAPTER XXIV 

THE STUDY OF OLD PAINTINGS AND DRAWINGS 

The study of old pictures, with the view of discovering 
the causes of the physical and chemical changes which 
have taken place in them, is fraught with interest. The 
material on which they are executed, the medium em- 
ployed, the pigments which can be identified, and the 
varnish which has been applied to the surface, all these 
matters demand attention. The dates of the various 
works examined, the countries in which they have been 
produced, the conditions under which they have been 
preserved, and the treatment to which they have been 
subjected, constitute elements in the investigation which, 
whenever possible, should be kept in view. But the 
adequate treatment of this extensive subject requires 
not a brief chapter, but a whole volume. And then our 
materials, though in some directions most abundant, are 
in great measure inaccessible. We must confine our 
attention to such specimens as are shown in our public 
galleries. Even then we find ourselves hampered by the 
impossibility of making the thorough investigation which 
is desirable, and by the too frequent absence of certain 
important data. In the present chapter we limit ourselves 
to some general remarks, and to a few brief observations 
upon a certain number of pictures in the National 

32s 



326 CHANGES IN PICTURES 

Gallery, the National Portrait Gallery, and the Victoria 
and Albert Museum ; and our selection will be confined 
to paintings in oil, tempera, and water-colour, as the 
available works in fresco in England are too few and too 
fragmentary to furnish the information for which we are 
seeking. 

It will hardly be necessary, with respect to changes 
in painting-grounds, to do more than refer the reader to 
what has been already said on this subject in Part I. of 
the present work. The causes of the decay of panels and 
of the convexity which their painted surface shows in so 
many cases have been already discussed. The disruption 
of the ground and of the superposed layer of paint con- 
sequent upon this convexity needs no further explanation. 
The staining of the white priming which has been laid on 
certain kinds of wood has been traced to dark-coloured 
exudations of soluble organic matters. The grain of 
some kinds of wood, notably of oak in pictures of the 
Dutch and Flemish schools, often becomes painfully con- 
spicuous in course of time, and gives to the surface-cracks 
a peculiar character. The microscopic structure of 
certain woods and the peculiar distribution of their histo- 
logical constituents serve to explain these appearances. 
The causes of the decay and cracking of gesso-grounds 
in which size has been used, and the injurious mechanical 
and chemical alterations which paper and primed canvas 
may exhibit, have been already touched upon. The 
other conspicuous changes which may be observed in 
old pictures are connected with the medium, the pig- 
ments, or the varnish. All these matters have been 
referred to in Parts II. and III., yet there are three points 
on which further discussion may not be out of place. I 
refer to the number and character of the pigments used 



OLD PAINTINGS 327 

in early works, to the manipulation of the paint, and to 
the employment of white lead. Now, the pigments to 
which the earlier painters were restricted were not only 
few in number, but were mainly of mineral origin. At 
the first glance one sees that the Italian artists of the 
thirteenth century, and of the first half of the fourteenth, 
worked almost exclusively in natural inorganic pigments, 
two of which stand out in their works in startUng promi- 
nence, namely, vermilion and ultramarine ; and their 
pigments were nearly all opaque or semi-opaque. The 
absence of any pure and brilliant yellow, opaque or 
transparent, from their pictures is another noticeable 
characteristic. In the works of Jan van Eyck and 
Rogier van der Weyden, and in those of many of the 
Italian painters of the fifteenth century, the range of 
colours is more extensive. Pigments which could not be 
used in tempera or size, or which were semi-opaque when 
employed with these vehicles, gave great richness and 
variety to their works in oil. This tendency to press 
into the service of pictorial art other coloured materials 
besides those of mineral origin, namely, animal and vege- 
table pigments in considerable variety, became more 
marked as time went on. And during the nineteenth 
century the progress of synthetica,! chemistry placed at 
the disposal of the picture-maker a long series of pigments 
— good, bad, and indifferent, — so that the chances of 
introducing dangerous and fugitive colours have been 
enormously increased. It is to this increase in the 
number of pigments, and to their greatly extended range 
of composition, rather than to their mode of preparation, 
that one should attribute in great part the frequent 
deterioration of modern paintings. 

But the second point to which reference has been made 



328 OLD PAINTINGS 

is concerned with the mode of laying on colours. The 
exquisitely minute and careful manipulation of Jan van 
Eyck, of Fra Giovanni Angelico, of Hans Memlinc, of 
Gerard Dou, of Gerard Terborch, and of many another 
old master, could not have been hurried. It was solid 
but smooth ; the paints hardened gradually into one 
organic whole. And we could name several oil-painters 
of the eighteenth century, and even of the present day, 
whose work is executed in the same safe manner, and 
which, were it not for the occasional introduction of 
dubious materials, would be sure to remain sound for 
hundreds of years, provided, of course, that the painting- 
ground be satisfactory. But this careful mode of painting 
does not suit the temperament, nor is it capable of 
expressing the ideas of many artists. The thick impasto 
and loaded colour, the eflfective brush-work, the juicy 
pencil, and the dashing haste of several painters often 
prove to be elements of danger. 

The third point, concerning which a few remarks seem 
advisable, is connected with the use of flake-white. There 
are many old oil-paintings in which the only perfectly- 
preserved parts of the v/ork are those in which flake- 
white has been used with considerable freedom. Here 
the continuity of the layer of pigment is intact, elsewhere 
there are cracks and roughnesses and scalings-ofF. To 
what cause is the preservation of the high lights and of 
the paler flesh-tints attributable ? The association of 
hardness and cohesiveness which these parts show is 
traceable to the white lead. This pigment was formerly 
always prepared in such a way as to contain a consider- 
able quantity of lead hydrate. The particles of this 
hydrate do not lie, as it were, side by side with those 
of the chief constituent (the lead carbonate), but are so 



ACTION OF WHITE LEAD 329 

united with the latter as to form one complex compound. 
This compound acts upon the linseed or other drying oil 
with which it is ground, forming a substance of great 
hardness and durabihty. 

This substance — that is, the entire mass of the white- 
lead ground in oil which has become solid, tough, and 
hard — seems to contain a small percentage of a lead- 
soap, formed probably out of the free fatty acids of the 
linseed-oil. But whatever the complete explanation of 
this hardening action may prove to be, there can be no 
doubt that we must attribute to the simultaneous presence 
of oil and the hydrato-carbonate of lead the preservation 
of the continuity of surfaces of the whites, and of the pale 
tints into which white lead enters, in many an old picture. 
No other pigment in common use is capable of solidifying 
the admixed oil to anything like the extent that character- 
izes white lead. Now there are modern preparations of 
white lead made chiefly by precipitation or the ' wet way,' 
which produces a pigment containing little or no lead 
hydrate. Some writers on pigments advocate the use 
of these newer products. ' Why,' say they, ' should you 
carefully exclude from your pictures oils, and varnishes, 
and siccatives which contain lead in solution, and then 
introduce the same or a like substance in your white lead 
ground in oil ?' Many years ago I tried to answer such 
a question as this by means of experiment. I was actu- 
ated by a desire, based on theoretical considerations, of 
preventing altogether the formation of lead-soaps. I 
tried comparative experiments with zinc oxide, pure lead 
carbonate, and the Dutch-made lead hydrato-carbonate, 
or ordinary flake-white. The two lead pigments (with 
which alone we are now concerned) were washed 
thoroughly with distilled water and dried before being 



330 ACTION OF WHITE LEAD 

ground in linseed oil. The oil-paints thus prepared were 
spread in duplicate series upon glass, paper, and primed 
canvas ; one set was kept in a dark box, the other was 
exposed to strong light. So decided was the superiority 
of the ordinary flake-white over the pure carbonate, when 
both series of specimens were examined after the lapse of 
various intervals of time, that I was reluctantly compelled 
to abandon my recommendation of the latter. Ease in 
working, solidity of body, and rapidity of drying, were 
not the only points of superiority ; for the films of paint, 
after having been kept a year, showed differences in 
hardness and in smoothness of surface which were all in 
favour of the hydrated carbonate. No discoloration was 
observed in the specimens exposed to light, except in the 
case of the pair upon paper ; the absorbent ground had 
withdrawn some of the protecting oil, and both specimens 
had equally darkened. In darkness all the specimens 
had become of a somewhat greyish yellow, the discolor- 
ation being about equal in all the pairs, the pair spread 
on paper having, as in the previous case, become darker 
than the others. The late Mr. G. W. Wigner tried a 
somewhat similar series of experiments, and came to the 
same conclusions. I should add that these deductions 
were corroborated by the results of other trials, in which 
numerous permanent coloured pigments mixed in pale 
tints with these two lead whites were treated in the same 
way. If, however, we feel bound to recommend the 
ordinary flake-white instead of pure lead carbonate, that 
recommendation does not prevent us from excluding lead- 
containing oils from our pictures, seeing that we possess 
perfect substitutes for them, and that there is no reason 
for thus multiplying the causes of possible change. 

Before commenting on some of the lessons to be drawn 



ILLUMINATED MANUSCRIPTS 331 

from individual pictures, it may be desirable to make a 
few observations on some of the changes frequently ob- 
servable in old illuminated manuscripts and choral books. 
The tarnishing of lead and copper pigments laid on with- 
out any protection but that of gum is very frequently 
seen. The darkening of vermilion is apparently capri- 
cious,* but is really explicable in part by the substitution 
of red lead for vermilion, and in part by the molecular 
change which the latter pigment is known to suffer, and 
which has been already described. Ultramarine always 
stands out absolutely intact ; sometimes it acquires extra- 
ordinary prominence by reason of every other pigment 
on a page having altered. The red cochineal and kermes 
lakes have either gone or become paler and brownish. 
Sometimes fruits painted in vermilion have been shaded 
or dotted with a crimson lake, but the latter has dis- 
appeared, leaving nothing but a slight gummy appearance 
upon the scarlet ground. Blue flowers painted in smalt 
and veined with indigo show scarcely a trace of the latter 
pigment. Verdigris, which is partly soluble in water, 
has run and discoloured the vellum, and at the same time 
has acquired a brownish hue. Sap-green, from buck- 
thorn berries, has faded greatly. Lilien-griin (of the 
seventeenth century), from the flowers of Iris germanica, 
has disappeared. 

We now cite a few pictures, out of a large number 
which have been studied for the purpose of observing the 
present state of the materials which have been used in 
their production. We begin with some works in the 
National Gallery, Trafalgar Square. 

* An initial letter in vermilion, painted in the fifteenth century, 
and perfectly unchanged, became black by one year's exposure to 
sunshine. 



332 OLD PAINTINGS 

Margaritone di Magnano (1216-1293). No. 564. In 
the very limited palette of this early painter in tempera 
we note that the vermilion, a yellow earth, lamp-black 
and a puce colour are well preserved ; the last-named 
pigment may be a form of iron oxide, and corresponds 
in hue to the artificially prepared oxide called ' Mars 
violet.' 

Giovanni da Milano (late fourteenth century). No. 
579A. The crimson on the robes of two of the three 
figures which occupy these panels seems to be derived 
from madder, and is well preserved. 

Jan van Eyck (1390 ?-i44i). No. 186 (dated 1434). 
The green robe in this famous picture shows distinct 
cracks, which differ in character and are larger in size 
than any others in the work. The flesh-tints are per- 
fectly preserved as to texture. I suspect that verdigris 
has formed a constituent of the green paint employed. 

Fra Giovanni Angelico (1387-1445). No. 663. The 
translucent reds and purples in this work have faded 
somewhat ; the green, which appears to be malachite — 
' green bice ' — has stood. On the whole this exquisite 
work in tempera is remarkably well preserved. 

Dierick Bouts (1410 ?-i475). No. 664. Painted on 
linen which had received a very thin priming ; the pre- 
servation of this work, which has never been varnished, 
is remarkably good except in two particulars — the red 
pigment used for the sleeves, linings of robes, etc., having 
faded, and the white paint on the dress of the Virgin 
having partially scaled off. From certain peculiarities 
in the touch, and from the minutely wrought details of 
the landscape, I conclude that the medium used could 
scarcely have been the usual egg-yolk tempera, but was 
rather a thin size. 



OLD PAINTINGS 333 

Bennozzo Gozzoli, School of (fifteenth century). No. 
591. The vermihon in this tempera picture is preserved 
in startling brilliancy ; the translucent reds have become 
rather faded and embrowned. 

Melozzo da Forli (1438- 1494). No. 755. It is prob. 
able that verdigris v^as employed in painting the green 
carpet in this work. If so, the cracks in this part of the 
picture (more conspicuous here than in other parts) would 
be due to the corrosive action of this dangerous pigment. 

Tuscan School (end of fifteenth century). No. 781. 
The lining of the cloak of Tobias in this picture seems to 
have been painted with verdigris ; it is now very dark, 
in parts nearly black, although the pigment used has 
evidently been mingled with much protective resin, as its 
thickness is excessive when compared with that of other 
parts of the work. 

Gregorio Schiavone (fi. 1470). No. 630. The madder 
and vermilion in the robe of one of the figures in this 
tempera picture are well preserved. This is also the 
case in another work by the same artist in the author's 
possession. 

Gheeraert David (1460- 1523). No. 1,045. The fine 
crimson glazings of madder-lake in this oil picture are in 
perfect preservation. The same remark may be made 
concerning another picture (No. 1,432) by the same artist. 

Michelangelo Buonarroti (1475-1564). No. 790. This 
unfinished tempera picture affords an instance of the 
stability of vermilion mixed with red-lead (in the robe of 
one of the figures), of terre verte and of madder-lake. 
The last-named pigment is also to be noted in the well- 
preserved hatchings and stipplings on the robes of two of 
the angels in No. 809. 

Ridolfo del Ghirlandaio (i 483"! 561). No. 1,143. This 



334 OLD PAINTINGS 

oil picture, originally painted on wood but transferred to 
canvas, has been repaired and repainted in several places. 
But the red glazings, apparently madder-lake, and the 
green colour, seemingly verdigris on malachite, are, if 
original, well preserved. The preservation of verdigris 
when glazed on malachite is not unusual ; the two pig- 
ments are closely related chemically, and are not likely 
to react upon or injuriously affect each other. 

In the National Gallery there are ten portraits in wax- 
pigments from the Hawara Cemetery in the Fayum, 
Egypt. A few of these portraits from this Cemetery are 
on canvas, but the great majority on panels of wood. 
There is a rich purple paint in several of these works, a 
purple which one might perhaps be inclined to identify 
with Tyrian purple from Purpura lapillus and other mol- 
luscs, but which the examination of certain specimens of 
ancient pigments leads one to conclude to be a madder 
derivative. Anyhow, it has lasted, apparently unchanged, 
for some eighteen centuries. But it must be remembered 
that these remarkable paintings (Nos. 1,260-1,265, and 
1,267-1,270) have been preserved in darkness almost from 
the time when they were executed by Roman artists in 
the period 80 to 180 a.d. The other pigments in these 
paintings are yellow, red and brown ochre, charcoal 
black, a blue consisting of a copper-calcium silicate, a 
green from malachite, and perhaps verdigris also. An 
orange-red pigment may be either red lead or realgar. 
The pigments, incorporated with wax, were laid on, in a 
fused condition, upon a distemper priming. 

It happens that some information as to the pigments 
actually employed by a Greek or Graeco- Roman artist of 
the second century is furnished by six specimens found in 
one of the Hawara graves by Professor W. M. Flinders 



OLD PAINTINGS 335 

Petrie. These pigments were : white, mainly gypsum ; 
yellow ochre having, however, almost the precise hue of 
true antimony yellow ; red lead ; dark red due to ferric 
oxide ; pink, probably derived from madder ; and the lime- 
copper silicate, known as Egyptian blue. 

As to British pictures in the National Gallery, we can 
afford space for a few words only. The works of Sir Joshua 
Reynolds generally show the fading of the crimson lake 
(from cochineal) in the flesh tints, the vermilion and 
mineral yellows alone remaining. The picture of the 

* Infant Samuel ' may be cited as an example of the large 
and wide cracks caused by the free use of bitumen (in the 
dark background). Two paintings by J. M. W. Turner 
may be particularly mentioned. In No. 560, * Chichester,' 
the bright lake-reds in the sky have become reduced to 
brown stains — anything but luminous. In No. 534, the 

* San Benedetto, looking towards Fusina,' we notice how, 
in a group of small clouds near the top of the picture, 
where vermilion and lake have been introduced, the 
vermilion remains, but the lake is now a pale yellowish 
brown. 

The good condition of the great majority of the pictures 
in the National Gallery of British Art at Millbank is worthy 
of note. In this category may be placed the works of 
Mr. G. F. Watts, R.A., and a number of other paintings 
out of which I select a very few for special mention. ' The 
Death of Chatterton,' by Mr. Henry Wallis (No. 1,575), 
painted in 1856, was retouched subsequently, so far as 
the breeches of the dead poet are concerned, the crimson 
lake originally employed having practically perished. 
No. 1,685, < Christ Washing St. Peter's Feet,' by Ford 
Madox Brown, was completed half a century ago. It 
shows, so far as one can judge, no signs of deterioration. 



336 OLD PAINTINGS 

Of ' The Annunciation,' by D. G. Rossetti (No. 1,210), 
painted in 1849, the same observation may be made. 
Anyone familiar with Lord Leighton's practice and with 
his extreme care in the choice of permanent pigments, 
would not expect to see any change in No. 1,574, ' ^^^ 
Bath of Psyche,' a work, moreover, which was finished 
so recently as 1890. To the critic of pigments, paintings 
of flowers afford much information, partly because they 
are generally pitched in a very high key, and partly 
because the living flowers themselves are generally avail- 
able for comparison with their representations in paint. 
Two of the pictures by George Lance (Nos. 443 and 1,184) 
betray the free use made by this accomplished artist of 
such fugitive pigments as carmine, crimson lake, gamboge 
and yellow lake. 

We may now pass on to some instructive examples pre- 
served in the National Portrait Gallery : 

Marc Gheeraedts (1561-1635). No. 64. In this portrait, 
painted probably in 1614, while the vermilion has stood, 
the translucent reds appear to have faded and changed. 
The white sleeves of the dress are ornamented with small 
sprigs, which are now brown, and were probably originally 
painted in some vegetable yellow. The reddish pattern of 
conventional foliage on the cloak now clashes with the 
colour of the chair, the curtain, and the table ; the hues 
of all or some of these parts must have altered. 

Sir Peter Lely (1617-1680). No. 509. A well-preserved 
picture in most respects, but it is probable that crimson- 
lake has been used for the satin dress, which is now a 
pinkish grey, and clashes with the flesh tints. This work 
was probably painted about 1669. 

William Hogarth (1697- 1 764). No. 289. This portrait 
of Hogarth, painted in 1758 by himself, affords some in- 



OLD PAINTINGS 337 

formation as to the pigments he employed. He holds in 
his left hand a mahogany palette 'set' with eight colours. 
The first of these is white lead, and remains unchanged ; 
so also is the second, vermilion ; the third is a pale warm 
brown, precisely the hue of faded crimson lake ; the fourth 
is now nearly black and undeterminable ; the fifth is yellow 
ochre, slightly embrowned; the sixth is a pale yellow, 
well preserved — much like true Naples yellow; the seventh 
is a grey-blue, probably much changed ; and the eighth 
and last a fair lavender blue colour. The seventh pigment 
may have been indigo, and the last possibly smalt. The 
cap on the artist's head has certainly faded in colour; 
probably it was painted with cochineal lake. 

William Hoare, R.A. (1706-1792). No. 112. This por- 
trait of Alexander Pope, in coloured crayons on grey 
paper, shows the blues apparently intact. 

Thomas Phillips, R.A. (T770-1845). No. 269. This 
portrait of Faraday, painted in 1842, shows a large number 
of cracks, many of them wide. Where flake-white has 
been introduced somewhat freely, as in the face and hands, 
the shirt and collar, and the galvanic battery on the table, 
the paint has not lost its continuity. 

John Partridge (1789-1872). No 342. ' Meeting of the 
Royal Fine Arts Commission.' This picture was painted 
in 1846. Almost every part of it is very badly cracked 
through the use of bitumen, and perhaps also of much 
megilp. Even the shaded portions of the faces have not 
escaped, although the high lights have been preserved 
where the proportion of white lead present has been large. 

Many instructive illustrations of the degrees of stability 
shown by pigments are furnished by examples in the 
Wallace Collection at Hertford House. 

Philippe de Champaigne (1602-1674). No. 119. This 



338 WA TER-COLO UR DRA WINGS 

picture is remarkable not only for the perfection of its 
technique, but for the extraordinary state of conservation 
of all the pigments, which cover a wide range of colours, 
and include a transparent amber-yellow and a rose. 

Sir Joshua Reynolds (1723- 1792). No. 47. Here the 
fatal asphaltum asserts itself, the background resembling 
a dissected map. 

J. L. E. Meissonier (1815-1891). No. 291. Generally 
the works of this careful painter are well preserved, but 
in this small example there are to be seen a few thin long 
cracks, which seem to have arisen in consequence of the 
premature application of varnish to the picture before the 
oil-paint was hard. 

In Sir John Soane's Museum the two fine series of well- 
preserved oil-paintings by W. Hogarth (1697- 1764) will 
repay careful study from the point of view now being 
considered. 

The remaining works to which attention is now called 
are a few of the water-colour drawings shown in the 
Victoria and Albert Museum. 

William Daniell, R.A. (1769- 1837). In one of the 
water-colours by this artist the blue and green elements 
have disappeared, save just in one little bit of smalt blue 
in a sailor's clothes. In another drawing the sky is now 
a mere dirty laboured stain. 

William Green (1761-1823). No. 685. An iron red 
has here become too prominent. 

Samuel Howitt (1765-1822). No. 3,019, 1876. Ap- 
parently well preserved, but, on further scrutiny, it seems 
that the ultramarine in the shaded parts of some of the 
rocks and trees stands out more prominently than it 
could have done originally. 

Anne Frances Byrne (1775-1837). No. 1,358, 1874. 



WATER-COLOUR DRAWINGS 339 

In this fruit and flower piece the indigo in the sky has 
gone, while the yellow pigments and the red lakes have 
suffered greatly ; the roses are blanched, and the purple 
grapes have lost their crimson element. 

John James Chalon, R.A. (1778-1854). No. 570. The 
' River Scene in Devonshire,' painted in 1808, shows the 
shaded parts of the clouds pink, from the loss of indigo. 
The hills are now too pale for the trees dotted upon them, 
through the fading of sap-green and gamboge, which have 
been used in painting the grass. The shadows under the 
ripples of the water have greatly altered, from the change 
of indigo and other pigments ; they now show dirty stains 
and elaborate brushwork. 

No. 54, 1887, 'At Hampstead Heath,' by the same 
artist, is, on the other hand, a well-preserved drawing, 
which has been more recently acquired by the museum. 
The blues are particularly good, although the vegetable 
yellows may perhaps have faded somewhat in spite of 
the care which has been taken with the drawing. 

John Cristall (1767- 1821). No. 142, 1890. This 
drawing seems to have kept its hues well, and affords 
a good example of the style of colouring of the period 
and school to which it belongs. 

Jacob Xavery (painted in 1757). ^o. 15, 1872. This 
has faded woefully. The sickly peaches and spectral 
grapes proclaim the evanescence of crimson lake, gam- 
boge, and indigo. 

Mary Moser, R.A. (1744-1819). No. 160, 1881. Very 
little is left of the original colour here ; the ' roses and 
other flowers ' are a complete wreck. 

Francis Danby, A.R.A. (1793-1861). No. 480. The 
blue in the sky unchanged, but the pigments which once 
modified its hue have fled. 



340 WA TER-COLO UR DRA WINGS 

John Varley (i 778-1842). No. 381. Hot iron reds 
show themselves in great force in clouds and elsewhere — 
even in the river ; the modifying organic pigments with 
which they were mixed have nearly disappeared. 

George Cattermole (i 800-1 868). No. 503. The crimson 
lake seems to have faded from the face in this drawing. 
In No. 507, painted in 1850, we have a good illustration 
of the warm brownish hues produced by the deterioration 
of crimson lake. 

Samuel Prout(i783-i852). Nos. 1,473, 1869, and 3,056, 
1876, afford examples of the stability of true ultramarine. 
The skies in both these drawings are now quite out of 
harmony with the architectural features, some of the pig- 
ments in which must have faded. These drawings should 
be compared with others by the same artist which hang 
beside them, and in which the blues of the skies, as well 
as some of the pigments in other parts, have faded. Here 
it may be convenient to remark upon the startling prom- 
inence of the skies, and sometimes of the blue distances, 
in many water-colour drawings. The first glance on 
entering a room in which such works are gathered reveals 
the permanence of ultramarine and cobalt blue, the latter 
pigment being, of course, of comparatively recent intro- 
duction. But the want of harmony in such drawings 
furnishes evidence at the same time of the decay of many 
other pigments — of liquorice and tobacco-juice, of yellow 
lake and brown pink, of indigo and rose pink. 

William Henry Hunt (1790-1864). No. 1,031, 1873. 
Some of the ruddy hue from the cheeks of the boy appears 
to have gone. In 1,525, 1869, some of the pink in the 
apple-blossom has faded ; the primrose-flowers are greener 
and less yellow than they once were, probably from a 
change in lemon yellow. The l^awthorn-blossom in 1,470, 



WATER-COLOUR DRAWINGS 341 

1869, has lost the faint rosy blush that was once visible 
in some of the flowers — a delicate hue which I can dis- 
tinctly recall. 

The above examples, selected almost at random, must 
suffice. But I may point to a different kind of injury, 
from which water-colour drawings sometimes suffer, by 
citing the case of W. Delamotte's * View of Christ Church, 
Oxford.' This seems to have been pasted on wood, and 
to have been stained in consequence ; at least, it appears 
likely that the brown spots in the sky may be traced to 
the mount. A work by T. Barker (No. 134, 1878) and 
the * Dieppe' of J. S. Cotman (No. 3,013, 1876) furnish 
additional examples of the same kind of damage. 



CHAPTER XXV 

CONSERVATION OF PICTURES AND DRAWINGS 

It is generally conceded that a finished oil painting is 
best kept in such a position that it is exposed to daylight 
of just sufficient intensity for it to be well seen, the direct 
beams of the sun being excluded. In darkness, or even 
in approximate darkness, the lead-whites may tarnish, 
and the oil and resins darken. Even with the most 
moderate illumination, however, the more fugitive pig- 
ments, such as the cochineal and quercitron lakes, will 
in no long time alter and fade to such a serious extent 
as to destroy the ' keeping ' of the work. But there is 
really no need to introduce these evanescent pigments, 
for every nuance the artist can desire may be produced 
with paints having a sufficient if not perfect degree of 
permanence. The question of artificial lighting here 
comes in. Against oil lamps, properly constructed and 
managed so as to avoid the production of smoke and 
soot, nothing can be urged ; the same opinion may be 
given in reference to the use of electric incandescent 
lamps. The introduction of electric arc lamps seems 
less safe, even when the illumination they afford is reduced 
to the necessary minimum, for the light they emit is richer 
in those rays which, as a general rule, are peculiarly 
effective in bringing about chemical changes in the less 
stable pigments. But the light by which pictures are to 

342 



CONSERVATION OF PICTURES 343 

be seen is but one of the conditions out of several which 
have to be considered in their conservation, though 
perhaps the most important. The mode of securing a 
picture in its frame is not an altogether trivial matter. 
In the majority of cases the expansion and contraction 
with variations of moisture and temperature, of panel 
and canvas, do not correspond accurately with the similar 
changes of the frame. In consequence, too great rigidity 
in the system of fixing adopted should be avoided. Duly 
adjusted springs or blocks of indiarubber (not vulcanized), 
secured in the rebate, afford convenient means of obtain- 
ing the necessary freedom of movement, while preventing 
the jar caused by accidental concussions. An equable 
temperature is another important condition ; on no 
account should currents of hot or of cold air impinge 
directly upon the front or back of a painting. Moreover, 
this is not a mere question of temperature, for such 
currents of air may bring in particles of dust and other 
impurities, while their hygroscopic condition is sure to 
vary. This question of moisture is of some moment. 
For if freshly-warmed air, which is pretty sure to be 
comparatively dry air, is allowed to come in contact with 
panels or canvases, it will withdraw from them some of 
their necessary hygroscopic moisture, and thus cause 
capricious and hurtful changes of size. Such changes, 
often repeated, cannot but result in the production of 
cracks and fissures in the oil paintings subjected to these 
varying conditions. The hygroscopic balance between 
picture and air can be maintained only by a due supply 
of moisture to the warmed air before the latter comes in 
contact with the painting ; the warmer the air the more 
moisture must be added to it. The same reasoning 
applies to the entrance of cold air, but in this case, care 



344 CONSERVATION OF PICTURES 

must be taken that it is sufficiently dry not to deposit 
water upon the picture. For the purpose of regulating 
the hygroscopic condition of the atmosphere in a picture- 
gallery, the introduction of a dew-point thermometer is 
advisable. And there is another contrivance by means 
of which the presence of the right proportion of moisture 
in the air may be recognised A strip of drawing-paper, 
another of primed canvas, and another of mahogany, all 
three being in a normal hygroscopic state, are to be 
separately balanced by means of counterpoises. When 
the air gets too dry, the strips will rise, owing to their 
loss of water ; when excess of moisture is present, they 
will sink. So long as the equilibrium of the beams to 
the ends of which the strips are attached remains practi- 
cally true, the air may be regarded as in a satisfactory 
hygroscopic condition. Three pairs of ordinary apothe- 
caries' scales (or spring-balances) suffice for the construc- 
tion of this apparatus, which should be protected by a 
glass case to which the air has free access. This ques- 
tion of the due amount of moisture in the air — neither 
in excess nor in defect — has scarcely received the atten- 
tion it deserves. But it will be allowed on all hands 
that few conditions are more trying to pictures in oil or 
water-colour than those caused by currents of hot, dry 
air rising directly below them during the day, succeeded 
by currents of cold, moist air descending upon them 
down the surfaces of the walls at night. 

The covering of an oil picture with glass, whatever 
objections may be urged against it from an artistic point 
of view, certainly secures the protection of its surface 
from the solid and liquid and, to some extent, from the 
gaseous impurities in the air. But the backs of pictures, 
especially of those painted on canvas, are often forgotten, 



FRAMING AND MOUNTING OF PICTURES 345 

yet excess of moisture and deleterious vapours and gases 
often enter from behind, and seriously discolour the 
painting-ground, and even the paint itself. Mention has 
previously been made of methods by which this cause of 
injury may be prevented by means of a double canvas, 
or a layer of white lead in powder mixed with starch- 
water, applied to the back of the original canvas ; 
American leather cloth, or even parchment-paper, affixed 
to the frame behind is nearly as effective. 

A few words only are requisite as to the mounting and 

framing of water-colour paintings. On no account must 

the back of the paper on which a drawing is executed 

come into contact with any kind of w^ood, or even with 

an inferior sort of paper or mounting-cardboard. Injurious 

substances in the latter may travel forwards into the 

painting-ground, and affect the pigments, while wood may 

cause stains. Iron brads produce rust-spots. Flour-paste 

is not a sound material for mounting drawings ; far better 

is an antiseptic size, which may also be used for fixing to 

the back of the frame the sheet of paper which is there 

placed to exclude dust. If we could secure a water-colour 

drawing from dust, and yet allow of the escape of any 

water set free in the form of vapour when the drawing 

gets, from whatever cause, somewhat warmer than usual, 

we should have effected an improvement upon the ordinary 

plan of framing. In this, the moisture liberated from the 

paper and mount cannot escape, but condenses upon the 

glass when it cools, only to be reabsorbed by that surface 

of the paper which carries the pigments, where it favours 

chemical and physical changes, until the hygroscopic 

equilibrium of the whole system — frame, mount, lining, 

paper, etc. — is once more re-established. I have used 

with advantage grey linen in lieu of brown paper at the 



346 PRESERVATION OF DRAWINGS 

back of frames, and, by means of a few strips of thick 
drawing-paper, have established an air-communication 
between the space in front of the drawing and that at 
the back. Thus the ventilation of the system is arranged 
for, yet dust is excluded. To hermetically seal a framed 
drawing, to the entire exclusion of all moisture and all 
air, is not possible. That under such conditions a greatly 
increased number of pigments would prove unalterable 
has been long known. We should add to these observa- 
tions upon the conservation of works in water-colour that 
they should certainly be kept in a rather drier atmosphere 
than that recommended for oil paintings. 

The plan of preserving the water-colour drawings of 
Turner, devised by the late John Ruskin, may fitly be 
mentioned here. It was described in a letter to the 
editor of the Times (October 28, 1856). The recom- 
mendation is to enclose each work in a light wooden 
frame, under a glass, the interior surface of which is pre- 
vented from coming in contact with the drawing by 
means of a raised mount. A number of such frames 
(five to fifteen) are kept together in cases, which can be 
carried or wheeled to any part of the room where the 
drawings are to be studied. Each frame slides vertically 
into grooves in the case. Professor Ruskin's reasons 
include the following : ' A large number of the drawings 
are executed with body colour, the bloom of which any 
friction or handling would in a short period destroy.' 
This argument, it will be seen, is directed against the 
keeping of such works, in their unframed state, in port- 
folios. Another reason given by Mr. Ruskin is that in 
the case of these drawings * their delicate tones of colour 
would be destroyed by continuous exposure to the light, 
or to smoke and dust.' He fortifies his position in refer- 



PRESERVATION OF DRAWINGS 347 

ence to such exposure in a letter to the Literary Gazette 
(November 13, 1858), in which he says that 'the officers 
of both the Louvre and of the British Museum refuse to 
expose their best drawings or missal-pages to light, in 
consequence of ascertained damage received by such 
drawings as have been already exposed ; and among the 
works of Turner I am prepared to name an example in 
which, the frame having protected a portion, while the 
rest was exposed, the covered portion is still rich and 
lovely in colour, while the exposed spaces are reduced 
in some parts nearly to white paper, and the colour in 
general to a dull brown.' ' That water-colours are not 
injured by darkness is also sufficiently proved by the 
exquisite preservation of missal paintings, when the 
books containing them have been but little used. Observe, 
then, you have simply this question to put to the public : 
" Will you have your Turner drawings to look at when 
you are at leisure, in a comfortable room, under such 
conditions as will preserve them to you for ever, or will 
you make an amusing exhibition of them (if amusing, 
which I doubt) for children and nursery-maids ; dry your 
wet clothes by them and shake off the dust from your 
feet upon them for a score or two of years, and then send 
them to the wastepaper merchant?"' Mr. Ruskin in 
another letter to the Times, which appeared on October 21, 
1859, wrote thus : ' I take no share in the responsibility 
of lighting the pictures either of Reynolds or Turner with 
gas ; on the contrary, my experience would lead me to 
apprehend serious injury to those pictures from such a 
measure ; and it is with profound regret that I have 
heard of its adoption.' Although considerable weight is 
rightly given to the opinions of Mr. Ruskin above quoted, 
it must not be forgotten that all paintings of the modern 



348 LIGHTING OF PICTURE-GALLERIES 

school are not to be classed with those of Turner and 
Reynolds in respect to susceptibility to the injurious 
action of the products of the burning of gas and of con- 
tinuous exposure to moderate light. When, therefore, 
Mr. Ruskin wrote (in the Daily Telegraph, July 5, 1876) : 
* I do not think it necessary to repeat my former state- 
ments respecting the injurious power of light on certain 
pigments rapidly, and on all eventually,' I find myself 
compelled to reject so sweeping an assertion. That light 
injures all pigments eventually cannot for one moment 
be conceded. And if we could but succeed in so modify- 
ing the light that illuminates our pictures as to remove 
from it certain particularly active beams, we might con- 
siderably augment the list of permanent pigments. 
Experiments on a small scale prove that several fluor- 
escent substances, such as a solution of quinine sulphate, 
while intercepting dangerous rays, do not sensibly modify 
the colour of the light, and yet lessen its chemical 
activity. In the first edition (published 1890) of the 
present handbook, I wrote : ' Possibly a transparent 
screen of this character will some day be used for our 
picture-galleries.' Since then an arrangement of coloured 
glass — peacock blue and yellow — has been devised by 
Sir W. Abney and introduced into one of the galleries of 
the Victoria and Albert Museum, with the object of pre- 
venting the entrance through the skylight of a great part 
of the injurious rays. Thirteen years ago I used the 
following words in relation to this subject : ' It is in- 
structive to note how much difference exists between 
different specimens of apparently colourless glass in their 
absorptive power for the so-called chemical rays. These 
differences may be tested by framing a strip of paper 
washed with carmine and covering it crosswise w4th the 



LIGHTING OF PICTURE-GALLERIES 349 

samples of glass to be valued, adding for comparison a 
plate of rock-crystal. Under the last-named material the 
fading is nearly as rapid as it is where the pigment is 
without any cover. It may be safely affirmed that 
miniatures should be protected by glass, not by rock- 
crystal. Further experiments on the selection of pro- 
tective glasses and the construction of transparent screens 
are needed. A partial discussion of this subject will be 
found in the next chapter, and to this I would refer my 
readers.' In this connexion a paper by Sir William 
Crookes, P.R.S., may be named. It was published in 
the Phil. Trans, of the Royal Society, Vol. 213 A, and is 
entitled ' The Preparation of Eye-Preserving Glass for 
Spectacles.' 

The question of the lighting of a gallery or room where 
pictures are to be displayed has been touched upon already 
at the beginning of the present chapter. We would now 
add that actual skylights are not without drawbacks. 
One of these, especially in the case of water-colours, is 
the presence in large proportion in the light from the 
zenith of those rays which act most energetically upon 
pigments, A few observations as to gas cannot be ex- 
cluded. Gas, before and after burning, is bad for pic- 
tures. The evil effects of an occasional escape of unburnt 
gas are less to be dreaded than those caused by the pro- 
ducts of gaseous combustion. These products are sul- 
phuric acid, sulphurous acid, carbonic acid, and the 
moisture which is formed at the same time. Thence 
results a hot, moist atmosphere laden with these corrosive 
compounds. The water- vapour condenses into the liquid 
form and dissolves a part of the acids named above ; the 
drops which trickle down are very injurious to paper, 
wood, canvas and pigments. In any case, all the pro- 



350 AIR IN PICTURE-GALLERIES 

ducts of the combustion of gas should be removed from 
the room as they are formed. For even when there may- 
be no visible condensation of liquid, the vapours formed 
are often absorbed as such by paper, canvas, etc., and do 
in that form their destructive work. An illustration of 
this fact is furnished by an analysis of the leather back 
of an old calf-bound volume. Owing to its absorption of 
the products of the burning of gas this back had decayed 
and fallen off, and was found to contain over 6 per cent, 
of free sulphuric acid. 

With respect to the building itself in which pictures 
are to be kept, our aim should be to secure as far as pos- 
sible pure air, an equable and agreeable but moderate 
temperature, and freedom from dust and dirt. Solidity 
of construction, a continuous damp-proof course, a certain 
degree of elevation above the ground-level, and double 
walls enclosing an air-space, are desirable as conducing 
to uniformity of temperature, and preventing the con- 
densation of moisture upon the interior of the rooms. 
Due provision should be made for excluding from the 
galleries themselves the dust and dirt which may be 
brought in by visitors. And it cannot be too strongly 
urged that the supply of fresh air should not, as it were, 
accompany the visitors, but be brought in from an inde- 
pendent source. The place of in-take of such supply 
should not be gratings near to, or on the level of the 
ground, in out-of-the-way and dirty corners, the certain 
depositories of uncertain rubbish. From such sources 
air laden with organic and inorganic impurities can alone 
come. The question of the exclusion of fog and city- 
smoke may be mentioned here. Some kind of air-filter 
is useful. It is astonishing how effectively the solid and 
liquid particles suspended in a yellow fog may be strained 



RESTORATION OF PICTURES 351 

off and intercepted by passing the air through a layer of 
loosely packed carded cotton enclosed between two sheets 
of perforated zinc — this air-filter of course requires 
occasional renewal. Moist white lead, that is, white 
lead in powder reduced to a paste by admixture with 
water, will absorb the sulphuretted hydrogen as well as 
the sulphuric and sulphurous acid present in town air. 
And if the walls of the galleries are coated with a dis- 
temper paint containing white lead, this absorption of 
impurities goes on continually. For these impurities are 
more readily absorbed by an unprotected and properly- 
prepared distemper than by the pigments in the pictures. 
To secure this result the distemper should be made, not 
with size, but with starch-water, just sufficiently strong 
to bind the particles together and to the wall. For 
further particulars as to these and other arrangements for 
the conservation of pictures, especially in public galleries, 
the reader is referred to a paper on the subject in the 
Portfolio for 1882, pp. 106-108. 

The conservation of pictures naturally leads us on to 
their restoration. Picture-restoration, like some other 
kinds of restoration, often involves injury, often renewal. 
It is frequently difficult, sometimes impossible, to re- 
establish the pristine state of the work. The operations 
involved should never be undertaken by the inexperienced 
amateur. And picture-restorers themselves are too often 
artists who have mistaken their profession, or who have 
been imperfectly trained. Many possess no power or 
appreciation of accurate draughtsmanship. Look, for 
illustrations, at those crucial parts, the hands and feet, 
in * restored ' pictures. Nor have they that exquisite 
sense of quality in colour and of delicate hues which will 
enable them to fill up properly actual gaps in a painted 



352 RESTORATION OF PICTURES 

surface. Then the pigments they use are too often un- 
safe, and their vehicles unsatisfactory ; so both soon 
alter, generally becoming darker and yellower. At the 
same time, the skill of some restorers in the matter of 
mechanical repairs — parquetting, transferring, relining, 
etc. — cannot be too highly extolled. 

Several manuals of directions for restoring pictures 
have been given to the world ; they are of very unequal 
value. Some of these tell you nothing, for they are 
intended merely to advertise the skill of the writers. 
Others advocate a treatment which may be called heroic, 
giving you solvents, not only for the discoloured varnish, 
but for glazings and paints. In reality, no directions can 
replace experience and skill. The late Max von Petten- 
kofer's method is one of the best known, but it is very 
rarely applicable with safety and success. The object of 
this method is the renewal of the transparency and con- 
tinuity of the varnish by a process of re-solution in situ. 
With this intention, the picture is exposed in a closed 
shallow box to the action of the vapour evolved from 
moderately strong spirits of wine. This vapour dissolves 
the mastic on the surface of the picture, forming once 
more a spirit-mastic varnish. This, on exposure to the 
air, hardens, and leaves a shining coat of resin. But this 
resin, being necessarily discoloured and sinking into the 
cracks of the paint, makes them more prominent, while 
there is great danger of its being unequally distributed 
over the surface of the work. 

When the varnish of an old picture is practically 
intact, but the surface is begrimed with soot and dirt, it 
should not be cleansed by the direct application of water, 
much less by the use of a solution of soap ; but a loaf of 
household bread, not more than a day old, should be 



RESTORATION OF PICTURES 353 

taken, and its crumb broken up into a tin canister fur- 
nished with a lid ; it is important that no pieces of crust, 
and no fragments of crumb which have become hard by 
drying, should be introduced. Then the crumbs should 
be shaken out, in portions at a time, from the canister on 
to the varnished surface, and rolled gently thereon by 
means of the fingers. By repeating this operation until 
fresh crumbs no longer become discoloured, it is often 
possible to improve the appearance of a picture very 
greatly. In any case, it affords a useful preliminary to 
the removal of the old varnish where such a further step 
is imperatively required. Such removal is effected by 
the mechanical process of chafing. A single tear of pure 
mastic resin is ground or crushed to fine powder, and 
placed upon some unimportant part of the surface of the 
picture ; but the operation may be begun without the aid 
of the mastic-powder. A gentle rotatory movement of 
the ends of the fingers soon reduces the old varnish-layer 
to powder, which is then removed by means of a soft 
badger-hair brush, or other suitable means. The work 
should be performed in a good light, and great care must 
be taken not to injure any tender glazings belonging to 
the painting itself. To ascertain whether the removal of 
the varnish has been carried far enough, the parts treated 
may be moistened with distilled water applied on a wad 
of carded cotton. When the operation is complete, and 
the surface is quite dry, a new coat of mastic-varnish 
may be applied, if possible in an artificially dried atmos- 
phere. Sometimes a little dragon's blood, or other warm- 
coloured resin, is added to the mastic- varnish, in order to 
prevent the cold and raw look which a picture which has 
lost its old toned varnish frequently presents. An oil- 
painting in which no megilp has been used, and which 

23 



354 REMOVAL OF VARNISH 

has received, a year after completion, the thinnest pos- 
sible layer of drying-oil containing a little copal- varnish, 
and then, after the lapse of a twelvemonth, its final coat 
of mastic-varnish, cannot be injured by the chafing pro- 
cess just described. And, even under less favourable 
conditions, it is the only method which can be recom- 
mended for general adoption. But it has its risks, and is 
not easily applicable in the case of pictures where the 
texture of a coarse canvas, or the grain of a panel, is con- 
spicuously evident on the surface. To these remarks on 
the chafing process, we may add that it is sometimes ad- 
visable to re- varnish a picture with fresh mastic before 
commencing to remove the old ; a day or two afterwards 
both layers may be removed together. 

The removal of old varnish by the use of solvents is a 
hazardous, though easy, operation. The liquid usually 
employed for this purpose is spirits of wine, of about 
60° overproof, diluted with one-fourth of its bulk of 
distilled water. It is applied by means of wads of 
carded cotton, the action of the solvent being arrested, 
when necessary, by instantly moistening the spot with 
spirit of turpentine on another wad, or, in some cases, 
with linseed-oil. But when mastic megilp has been 
used as the painting-medium, it also, as well as the 
pigments associated with it, may be removed by treat- 
ment with these solvents. And it must be remembered 
that some artists introduce layers or touches of water- 
colours in their oil-pictures ; these are almost certain to 
be affected by spirits of wine. Sometimes further injury 
to them may be arrested by the application of linseed-oil. 
Whenever a solvent is used in cleaning a picture, the 
cotton tufts employed should be examined carefully from 
time to time, in order to see that no actual pigment has 



RESTORATION OF PICTURES 355 

coloured them — that they are stained by nothing but the 
brown varnish. Other solvents besides those named are 
sometimes used in cleaning pictures, particularly where 
hard or oily varnishes have to be removed. Such sol- 
vents are acetone, fusel-oil, amyl-acetate, benzene, 
chloroform, and solutions of caustic alkalies. Great 
risk of injury attends their employment — indeed, the 
application of any kind of solvent is fraught with danger, 
and should never be attempted by the inexperienced. 

The usual plan of filling up actual gaps in the priming 
or gesso-grounds of old pictures is by means of plaster- 
of-Paris. When this has set, its surface is levelled by 
gentle attrition with a cork and dry whitening, or cuttle- 
fish. Great care is needed in order to prevent the 
pigments surrounding the place from being abraded. I 
have found asbestos-putty to be an excellent substitute 
for plaster in many cases ; its surface is made smooth 
and level by means of a painting palette-knife. But it 
cannot be tinted with water- or tempera-colours ; in 
order to make it match the hues of the neighbouring 
parts of the picture oil-colours must be used. In any 
necessary replacements of lost colours in old oil-paintings, 
it has been recommended to use not oil-colours, but 
water-colours, as these can always be distinguished from 
the old work, and, if necessary, removed; this can be 
done on ' stoppings ' of whitening and size, as well as on 
those of plaster. Tempera-pictures should, I think, be 
repaired with dry pigments mixed with egg-yolk, as in 
this case, when the final varnish is applied, a general 
harmony of effect is produced. If water-colours are 
introduced in repairing an oil-painting, the coat of varnish 
subsequently added is sure to deepen and darken them, 
unless this change has been allowed for during the pro- 



356 RESTORATION OF PICTURES 

gress of the work, by no means an easy thing to manage. 
When in any kind of repainting oil-paints are used, they 
should be mixed stiffly with a very little copal-varnish 
and spirit of turpentine, and should be rather lighter 
and less yellow in tone than the colours they are intended 
to match, since darkening and yellowing in some degree, 
however slight, are sure to occur subsequently. 

The cleansing and restoration of paintings executed in 
fresco require special care. Additions to supply colour 
which has scaled ofT are best made in tempera. When a 
fresco has become grimy by exposure to the smoky air 
of a city, methylated spirits of wine, applied freely on 
tufts of carded cotton, removes the tarry and sooty im- 
purities which a previous careful brushing of the painted 
surface has failed to dislodge. Attempts to clear the 
clouded portions of an injured fresco by means of dis- 
tilled water or aerated distilled water are usually attended 
with but slight success. The films which obscure the 
surface in such cases sometimes consist of sulphate of 
lime, produced from the carbonate of lime present by the 
action of the sulphuric acid occurring in the atmosphere 
of places where gas and coal are burnt. In getting rid 
of this somewhat opaque film by means of water, portions 
of the pigment are commonly removed. When a fresco 
has been dusted and then cleansed with spirits of wine it 
should be allowed to dry thoroughly, the lost colours 
renewed in tempera, and then the whole surface coated 
with a preparation of hard paraffin-wax. This prepara- 
tion, which has the consistency of an ointment, is made 
by melting together 4 parts of hard paraffin-wax 
(melting-point above 150° F.), i part of spirit of turpen- 
tine, and 15 parts of toluol. When cold, this mixture is 
to be spread uniformly over the painted surface, and then 



RESTORATION OF PICTURES 357 

allowed to remain until its volatile constituents have 
disappeared. Afterwards the paraffin -wax left on the 
surface is to be melted and driven in by the local applica- 
tion of a moderate heat. By this treatment the dead or 
matt surface of the fresco is preserved, the obscuring 
films are rendered translucent, and the picture may, 
when cleansing is again required, be safely sponged with 
pure water or weak spirits of wine. If any cloudiness of 
the surface still persists after the application of the 
paraffin-wax paste described above, the effect of treat- 
ment with the Gambler -Parry medium (see p. 142), 
largely diluted, may be tried. 

The treatment of an injured fresco, in accordance with 
the plan just outlined, was pursued in the case of Sir 
Edward Poynter's fresco painted in 1872-73 on the south 
side of the chancel in St. Stephen's Church, Dulwich. 
That the work done upon this damaged fresco has been 
successful may be learnt from the way in which 
Mr. James Ward wrote in 1909 of the then state of the 
painting in his book ' Fresco Painting,' on page 30. He 
there says that this fresco is ' in a perfectly sound con- 
dition, and is almost as fresh-looking and bright as when 
first painted ; ... it shows no sign of deterioration ; on 
the contrary, the surface looks, and feels to the touch, 
more like terra cotta, or of the texture and firmness of 
biscuit porcelain than anything else one can think of.' 
Mr. Ward would have come to a very different conclu- 
sion as to the permanence of fresco had he seen this 
painting when I took it in hand some four years before 
his approval was published ! 

An example of the treatment of a greatly damaged 
oil-painting on a plaster ceiling may be here cited. This 
work, in the Saloon of the Queen's House at Greenwich, 



358 RESTORATION OF PICTURES 

was painted between the years 1626 and 1635 by Orazio 
Gentileschi, a Pisan artist invited over to this country 
by Inigo Jones. It was reported in 1853 to be 'much 
damaged ' ; and fifty years afterwards, when I first 
examined it, its condition seemed well-nigh hopeless. 
The plaster ground had swollen, and had broken up and 
loosened the layer of oil-paint applied to it. This injury 
was due to the action of atmospheric sulphuric acid upon 
the calcium carbonate of the plaster. By spraying the 
whole surface with Gambier-Parry's spirit fresco medium 
considerably diluted, the coloured flakes which were 
ready to fall were secured in position, and then the lost 
portions were replaced by pigments ground in the same 
medium. These operations were carried out between 
the years 1907 and 1909. In cases of such serious 
damage as this of Gentileschi's ceiling, further treat- 
ments are necessary, as the injury to the plaster is a 



CHAPTER XXVI 

TRIALS OF PIGMENTS 

The testing of pigments for genuineness and for purity- 
has been discussed incidentally in Chapters XIII. to XIX. 
of the present volume. Though genuineness and purity"^ 
have often an important bearing upon the question of 
permanence, this last quality must be ascertained by 
independent experiments of another order. The study 
of old paintings often furnishes us with results of some 
value, the results of unintentional testings. But for the 
purpose of securing complete and wholly trustworthy 
information, we must know precisely all the materials 
and all the conditions of our trials. Not only must the 
painting -grounds, the mediums, and the pigments, be 
chemically examined, but we must be in a position to 
state the character of the atmosphere in which they have 
been exposed, and the nature and amount of the solar or 
other radiations to which they have been subjected. In 
the great majority of these trials accurate data as to 

* The chromatic values of pigments— their approach in hue, etc.^ 
to recognised standards of excellence — are not here taken into 
account. Such data may be obtained by the use of Lovibond's 
Tintometer when once the chromatic elements of a pigment in 
terms of the degrees of the standard glasses employed in this 
instrument have been determined. But really exact determinations 
of this kind require complex scientific apparatus, which cannot be 
profitably used except by an expert manipulator. 

359 



36o TRIALS OF PIGMENTS 

materials and conditions are wholly wanting ; even the 
South Kensington report affords us no information as to 
the composition of the pigments employed, nothing more 
than their commercial names, so that we have to take on 
trust their genuineness and purity. However, in this 
same most important series, quite unusual, if not un- 
precedented, care was taken in order to determine the 
conditions, physical and chemical, under which the pig- 
ments were tested. In my own experiments, carried on 
between 1856 and 1879, in somewhat desultory fashion, 
and extended and improved since 1880, the influence of 
purity of sample, of the presence of moisture and of oxygen, 
and of the nature of the * light,' has not been neglected ; 
the full details of the methods adopted, and of the results 
obtained, could not be appropriately introduced into an 
elementary manual. Mention will be made of the chief 
conclusions reached in the present chapter ; there are 
also numerous references to them in Chapters XIII. 
to XXII. 

In many early treatises on painting we find observations 
as to the degrees of stability possessed by various pig- 
ments, along with suggestions as to methods of treatment 
by which in certain cases greater permanency may be 
attained. To some of these observations and suggestions 
reference has been made in those chapters of the present 
volume which deal with pigments ; many of the remainder 
are now without practical importance, referring as they 
do to pigments which have been rightly discarded. 

It is only of recent years that trials of pigments have 
been made with any approach to exactness. But in the 
majority of cases no information has been secured con- 
cerning the purity and genuineness of the pigments with 
which the experiments have been made. I have not been 



TRIALS OF PIGMENTS 361 

able to find a single chemical analysis of any one of the 
pigments tested. The chromatic analysis of the light they 
severally reflect has, however, been recorded in the case 
of the water-colour paints examined by Dr. Russell and 
Sir W. Abney, who have likewise furnished some par- 
ticulars as to the intensity of the solar radiations to which 
the pigments were subjected. 

More than a century ago Sir Joshua Reynolds tested, 
in a rough way, the stability of some of the paints he 
employed. Two causes detract from the value of his 
results. In the first place, the information furnished con- 
cerning the nature of many of the pigments he tried is too 
imperfect to be of any use ; secondly, we are not ac- 
quainted with the conditions under which his specimens 
have been kept during the whole period since they left 
his hands. Two of his trial canvases are preserved in 
the Royal Academy. Although the darkening and em- 
browning of the surface are general, and though the 
names of the pigments employed are often undecipherable 
or meaningless, yet something useful remains. From 
the experiments made in 1772 we may gather the follow- 
ing facts : The proper hues of several pigments remain 
in a measure — orpiment, or kings' yellow in crystals ; 
yellow lake, with wax and drying oil ; gamboge, with 
lake and Venice turpentine ; gamboge, with (Venice) 
terpentine ; prepared gamboge, with wax ; and verditer, 
with varnish. On the other hand, gamboge with oil, 
lake with oil, and many other pigments of organic origin, 
when unmixed with wax or varnish, are names only, or, 
at the most, brown discolorations. 

M. J. Blockz, in his ' Peinture a I'Huile,' gives the 
results of a number of experiments made by M. J. Dyck- 
man. He condemns, for various reasons, not only asphalt, 



362 MR. ANDREW'S EXPERIMENTS 

but also terre verte, cobalt green, emerald green, raw 
sienna, raw umber, ivory brown, and all burnt madders. 
Cassel earth was slightly changed; brown ochre, burnt 
sienna, Mars brown, ivory black, and vine black, proved 
to be permanent. His lists of incompatible pigments are 
somewhat unnecessarily extended, not being justified, in 
all particulars, by further and more careful experiments. 
The experiments of the late F. W. Andrew, formerly 
of the Victoria and Albert Museum, have been carried on 
since 1876, but have been confined to water-colours, both 
moist and cake. His chief results will be found recorded 
along with my own, in Part HI., in the paragraphs 
devoted to the consideration of the several pigments. His 
water-colour washes, generally spread on Whatman paper, 
or Whatman board, were exposed for periods varying 
from twenty-eight to eighty-two months, in a south 
window, to all the sunshine available ; half of each wash 
was doubled back, and so far excluded from light. In 
some cases a third part of the coloured slip was exposed 
to the air and light without the protection of glass. The 
chief paints which were unaffected, at all events, so far 
as some specimens were concerned, by the exposure, are 
included in the following list : Yellow ochre, raw sienna, 
deep cadmium. Mars red, light red, Indian red, oxide of 
chromium, Leitch's blue, cobalt, artificial ultramarine, 
Prussian blue, raw umber, burnt umber. Naples yellow 
(true) became blackish in darkness, but was unaltered in 
light, while orange chrome showed dark patches. Further 
details must be given as to the pigments which were 
affected. In the tabular statements appended a selection 
from the results afforded by eleven sets of experiments 
is recorded, the letters C and M prefixed to the entries 
respectively denoting the employment of cake or moist 



TRIALS OF WATER-COLOURS 



363 



colours. The numerical values representing the residual 
hues are rough approximations only, but in some instances 
they were determined by means of comparisons with 
standard coloured liquids, contained in glass cylinders 
graduated into ten equal parts. Hellige's colorimeter or 
the tintometer of Mr. J. W. Lovibond, of Salisbury, may 
be employed with advantage in these estimations. 

CHANGES IN WATER-COLOURS 





Name of 


Months of 


Residual 


Depth Residual Hue 




Pigment 


Exposure 


{Original 


= 10) and Remarks 


M. 


Aureolin ... 


28 


10 


... Verges on orange 


M. 


Aureolin ... 


62 


10 


[yellow 


M. 


Aureolin ... 


82 


9 




C. 


Gamboge... 


28 


4 




M. 


Gamboge... 


28 


9 




M. 


Gamboge... 


82 


7 




M. 


Yellow lake 


62 


2 


. . . Yellowish grey. 


M. 


Yellow lake 


82 







C. 


Yellow madder . 


28 


I 




M. 


Yellow madder . 


28 


3 


... Pinkish grey. 


M. 


Yellow madder . 


62 


I 




C. 


Indian yellow . 


28 


... 8,9 




M. 


Indian yellow 


28 


9 




M. 


Indian yellow . 


60 


7 




M. 


Indian yellow 


82 


6 




M. 


Pale cadmium . 


82 


I 


... Palebufif. 


M. 


Vermilion 


62 


— 


... Blackish. 


M. 


Vermilion 


82 


— 


... Black. 


M. 


Carmine ... 


28 





... Pale grey. 


M. 


Crimson lake . 


28 





... Greenish grey. 


M. 


Burnt carmine . 


28 




... 


C. 


Pink madder 


28 






M. 


Rose madder 


28 






M. 


Rose madder 


62 


I 


... Pinkish grey. 


M. 


Rose madder 


82 




II 


M. 


Madder carmine 


62 


2 




M. 


Madder carmine 


82 







M. 


Purple madder . 


28 


4 


... A pale wash. 



364 



MADDER VERSUS COCHINEAL 



Name of 


Months of 


Residual . 


Depth Residual Hue 


Pigment 


Exposure 


{Original 


= 10) and Remarks 


M. Purple madder . 


62 


7 




M. Purple madder . 


82 


2 




C. Brown madder . 


28 


I 


Warm grey. 


M. Brown madder . 


28 


I 


II 


M. Brown madder . 


82 







C. Indigo 


28 


5 


... Greenish grey. 


M. Indigo 


62 


I 




M. Raw umber 


60 


9 


... Rather yellower 


M, Vandyke brown . . 


28 


7 




M. Vandyke brown . . 


60 


I 




M. Bone brown 


62 


8 





The pigments containing lead, such as the ordinary 
chromes, and those having a copper basis, Hke emerald 
green, had altered capriciously, losing part of their 
original colour, and becoming tarnished or embrowned in 
patches. Brown pink faded like the yellow lakes, but 
acquired a bluish-grey residual hue. 

The testing of the madder colours is so important that 
I introduce here a few additional experiments selected 
from my own note-books. The washes of the moist-colour 
paints were, as far as possible, of the same depth of tone, 
and they were all exposed together in a glazed frame to 
one year's sunshine : 



Nufne of 

Piginent 
Rose madder 
Madder carmine 
Madder carmine 

Madder red 
Purple madder 
Brown madder 



Residual Depth 
{Original = 10) 



Change of Hue, etc. 

Slightly more purplish. 

Almost unchanged. 

Much more purplish. This sample 

was from another source. 
Less red, more purplish. 
Duller, less red, more blue. 
Less red, more yellow-brown. 



In contrast to the above results with madder carmine, 
the following experiment with the ordinary carmine 



PROFESSOR ROOD'S EXPERIMENTS 365 

(prepared from cochineal) is instructive. On a sheet of 
Whatman paper, a space of 10 inches in length by 4 inches 
in width was covered with a uniform wash of the moist 
paint, having a depth of tint about equal to that of the 
petals of the old China rose. This coloured strip was 
then subjected to summer sunshine in such a way that 
successive single inches of its length received the Hght 
(during the same hours of similarly bright days) for periods 
of 2, 4, 8, 12, 20, 26, 30, 40, and 100 hours, one single 
inch at one end being, however, protected completely from 
all access of light. The exposure of 100 hours sufficed 
to bleach the last breadth completely, but had the rate of 
fading been in a simple arithmetical progression, a much- 
shorter exposure would have sufficed. In fact, the 
bleaching action was far more energetic during the first 
period of two hours than during the second, about 20 per 
cent, of the original colour having been destroyed during 
these two first hours, while during the second equal 
period the loss of depth did not exceed one-tenth of this 
amount. Moreover, it was noticed that the change of 
hue consequent upon the first exposure was different in 
kind to that which occurred subsequently. 

Professor O. N. Rood's Experiments. — In his ' Modern 
Chromatics,' pages 90 and 91, Professor Rood gives the 
results of a few trials which he made as to the effect on 
washes of water-colours laid on ordinary drawing-paper 
of three and a half months' exposure to summer sunlight. 

These pigments were unaffected : 

Cadmium yellow, yellow ochre, Roman ochre. 

Indian red, light red, Jaune de Mars. 

Terre verte. 

Cobalt, French blue, smalt. 

Burnt umber, burnt sienna. 



366 



PROFESSOR HARTLEY'S EXPERIMENTS 



The following pigments were all affected. The sequence 
represents the amount of alteration, the list commencing 
with those colours which suffered but little change : 



Name 


Nature 


Name 


Nature 


of Pigvtent 


of Change 


oj" Pigment 


of Change 


1. Chrome yellow 

2. Red lead - - 


Slightly greenish. 


13. Hooker's green - 


More bluish. 


Less orange. 


14. Gamboge - - - 


Fades, greyish. 


3. Naples yellow - 


Slightly greenish 


15. Bistre - - - . 


Fades, greyish. 




brown. 


16, Brown madder - 


Fades. 


4. Raw sienna 


Fades, yellower. 


17. Neutral tint - - 


Fades. 


5. Vermilion - ■ 


Darkens, brownish. 


18, Vandyke brown 


Fades, greyer. 


6. Aureolin - - - 


Fades slightly. 


19. Indigo .... 


Fades. 


7. Indian yellow - 


Fades slightly. 


20. Brown pink - - 


Fades greatly. 


8. Antwerp blue - 


Fades slightly. 


21. Violet carmine - 


Fades greatly, 


9. Emerald green 


Fades slightly. 




brownish. 


10. Rose madder - 


Fades slightly, pur- 


22. Yellow lake - - 


Fades _ greatly 




plish. 




brownish. 


II. Sepia - - • • 


Fades slightly. 


23. Crimson lake - 


Fades out. 


12. Prussian blue - 


Fades somewhat. 


24. Carmine • • - 


Fades out. 



Professor Rood adds that rose madder, brown madder, 
and purple madder were all a little affected by an exposure 
to sunshine for seventy hours, and that pale washes were 
completely obliterated by a much shorter exposure to sun- 
shine in the case of carmine, dragon's blood, yellow lake, 
gall-stone, brown pink, Italian pink, and violet carmine. 

W. N. Hartley's Experiments. — On September 4^ 
1886, the late Sir W. N. Hartley read, before the 
British Association at Birmingham, a paper on *The 
Fading of Water Colours.' His trials as to the effect on 
pigments of a comparatively brief exposure to intermittent 
sunshine in pure air may be thus summarized. Washes on 
the best drawing-paper were the subject of the experi- 
ments : 

Gamboge. — Pale washes were completely bleached in 
three days ; in a week strong washes were much lightened 
in colour, and rendered dull, even three hours' exposure 
producing a very visible effect. 

Crimson lake. — Six hours' exposure to sunlight and air 
almost bleaches pale washes, while three days or eighteen 
to twenty-four hours of intermittent sunshine cause dark 



PROFESSOR HARTLEY'S EXPERIMENTS 367 

crimson tones to become very much lighter, the hue of 
the pigment being altered. 

Light red. Indian red, and vermilion were unaffected. 

Olive green and brown pink were rendered lighter in 
colour by six hours' exposure, the former pigment be- 
coming bluish and the latter brownish in hue. 

Indigo, cobalt, and artificial ultramarine were unaffected. 

Brown madder became rather lighter after eight days' 
or forty-eight hours' exposure. 

Bistre faded with great rapidity, a light wash appearing 
much paler after six hours. 

Sepia. — A pale wash became colder in hue, but not very 
perceptibly paler. 

In a second series of experiments, sectors of paper discs, 
washed with various pigments, were enclosed between 
glass-plates, the edges of which were fastened with 
gummed paper. Under these circumstances, crimson 
lake and bistre were found to have been considerably 
altered by five hours' exposure — somewhat more so, 
indeed, than was the case when these pigments were 
freely exposed to the air. 

All the results above noted are in practical accord with 
those obtained by other observers. The exposure to 
intermittent sunshine ' for six hours a day during fourteen 
days,' does not produce a sensible effect upon vermillion 
and indigo. Had Sir W. N. Hartley extended his obser- 
vations a few weeks longer, his conclusions as to these 
pigments must have agreed with those which we have 
given, and therefore with the unanimous verdict of all 
other scientific observers. His statement that ' indigo is 
permanent' (British Association Report, 1886, p. 581) 
must, therefore, be modified into, ' indigo appears to have 
suffered no change after fourteen days' exposure to inter- 



368 PROFESSOR HARTLEY'S EXPERIMENTS 

mittent sunshine.' A similar alteration is demanded with 
regard to the stability of vermilion. 

Sir W. N. Hartley's experiments with water-colour 
washes on paper enclosed between glasses require a few 
words of comment. He is clearly and rightly dissatisfied 
with this method of trial. A supply of atmospheric 
oxygen, and of hygroscopic moisture, amply sufficient for 
large chemical alteration and oxidation of the enclosed 
pigments, was certainly present. And the glasses did 
accelerate the action, not because of ' the very slight tint 
of the plate-glass,' but in spite of it. This acceleration 
of change is mainly caused by the continued presence of 
moisture in the confined space between the two glasses — 
it cannot escape as it freely, and to a very great extent 
does escape, when a piece of tinted paper is exposed to 
sunshine in free air. I showed, indeed, in my lectures 
at the Royal Academy, so long ago as 1880, that the 
fading of many fugitive pigments is greatly lessened, when 
not altogether prevented, by enclosing the paper washed 
with them in a glass tube, the air of which is kept dry by 
means of some strongly hygroscopic substance. When 
both moisture and air are excluded (using a sealed 
vacuum tube), the suspension of fading and alteration of 
hue is still more marked and general. 

It should be added here that Sir W. N. Hartley found 
that cadmium yellow and Indian yellow are bleached by 
peroxide of hydrogen, and changed into a muddy yellow 
by sulphurous acid. This reagent bleaches artificial ultra- 
marine and dulls vermilion. He attributes the partial or 
complete destruction of the blue component of the hues 
in certain old drawings, which have been long exposed to 
air and light, to the presence of acids or acid substances in 
the air, in the paper, or in the red ferruginous pigments 
with which the blue colouring substances in question have 



MR. W. SIMPSON'S EXPERIMENTS 



369 



been associated. These blue pigments could have been 
nothing other than Prussian blue, indigo, or natural ultra- 
marine. I have ascertained, by direct experiments on old 
drawings, that the latter was but rarely employed for 
mixed tints, but it is quite probable that the reds prepared 
from colcothar, with which it may have been occasionally 
mingled, would sometimes contain enough acid salts 
(certain ferric sulphates) to destroy its colour. The pro- 
ducts of the burning of gas and of coal would also be rich 
enough in sulphuric acid to produce the same effect. I 
am unable to endorse Sir W. N. Hartley's statement that 
the best drawing-papers contain free sulphuric acid, at all 
events when fresh from the mill, but they soon acquire 
it when kept in an urban atmosphere. 

Mr. W. Simpson's Experiments. — Some washes of 
water-colour, of thirty-one different kinds, were made 
upon cards by the late Mr. W. Simpson. He so cut the 
cards as to divide each coloured strip in half ; one 
section was preserved in darkness, the other was exposed 
in an eastern aspect on the shutter of a house in London 
for fifteen years, but the sun did not shine upon the 
specimens after ten o'clock in the morning. As they 
were not tightly framed, the cards became a good deal 
discoloured by the absorption of noxious vapours and 
dirt. The results were : 



Na7ne 


Natu7-e 


Name 


Nature 


of Pigment 


of Change 


ofPigtnent 


ofChange 


Yellow ochre - 


None. 


Purple madder - 


Hue altered. 


Indian yellow 


Faded considerably. 


*Brown madder - 


Loss of redness. 


Lemon yellow 


None perceptible. 


Emerald green - 


Slight. 


' Newman's per 




Cyanine blue 


Apparently none. 


manent yellow 


None. 


*Prussian blue - 


None. 


Cadmium yellow 


Perhaps browner. 


French blue - - 


Faded very slightly. 


Chrome yellow 


Faded considerably. 


Cobalt - . - ■ - 


None. 


Brown pmk - 


Faded. 


Ultramarine - - 


None. 


Vermilion - - 


None. 


Indigo, rather 




Light red - - 


None. 


deep .- - - - 


Very pale grey. 


Indian red 


None. 


Burnt sienna - - 


None. 


Crimson lake - 


- Gone. 


*Vandyke brown ■ 


None. 


Carmine - - 


Gone. 


*Sepia - - . - 


Faded very slightly. 


Madder lake - 


More purplish. 


*Bistre . . . - 


None. 

24 



370 TRIALS OF PIGMENTS 

It will be noted that the above results are for the most 
part in agreement with those recorded by other experi- 
menters ; the chief exceptions are marked with a star. 
Vermilion is usually blackened, but it is possible that 
the sample employed in these experiments was the less 
changeable native form or cinnabar. The Vandyke 
brown, too, was probably the earthy rather than the 
bituminous variety ; the slightness of the change recorded 
for madder brown and sepia, and the absence of any 
alteration on the part of bistre, are less easy of explana- 
tion. The madder pigments seem to have stood more 
than usually well, but they often exhibit large differ- 
ences of stability. Nor must it be forgotten, in assigning 
values to the above results, that this trial of fifteen years' 
exposure was not of the severest kind. Although, on the 
one hand, there was the imperfect exclusion of an in- 
jurious London atmosphere, on the other hand, the 
energy of the solar radiation was much reduced by the 
prevalent condition of the smoky air, while the inter- 
mittent and capricious sunshine of the Metropolis never 
fell on the trial cards after ten a.m. 

The late Mr. R. H. Soden-Smith kindly placed at my 
disposal a large number of specimens of old water-colour 
cakes and of powder colours intended for oil-painting. 
One set consists now of eleven cakes or fragments 
of cakes (in their original box) bought about the year 
1815 of Newman, in Soho Square. This set is peculiarly 
interesting as the colours, which all bear the name of 
the maker and his device, represent those used by many 
of the best English water-colour painters during the first 
quarter of the nineteenth century. The cakes are : 
Indian yellow, raw sienna, raw umber, burnt sienna, 
burnt umber, vermilion, carmine, burnt carmine, pink 



SOUTH KENSINGTON REPORT 371 

madder, ultramarine, indigo ; neutral tint and sepia are 
missing. On comparing the hues of the first nine of 
these paints and of the indigo with the hues of the 
corresponding cake-colours as sold by the same house 
in 1886, no appreciable differences were detected save 
in the case of the raw umber. Here the pigment of 
1 815 showed a more beautiful nuance than that of 1886. 
On making comparative tests of the stability, under 
exposure to sunshine, of the two sets of pigments, the 
results were found to be practically identical. One cannot, 
therefore, claim for the water-colour paints in use one 
hundred years ago a degree of permanence greater than 
that possessed by their representatives of to day. 

By far the most important series of trials of water- 
colour paints yet published is that to be found in the 
report by the late Dr. Russell and Captain (now Sir W.) 
Abney to the Science and Art Department (1888). The 
reporters endeavoured to give precision to their ex- 
periments and their conclusions by a careful comparison 
of the effective radiation from different sources of light. 
The first part of their report contains a very useful 
discussion of the relative values of direct sunlight, light 
from clouds, and from an overcast or clear sky, and light 
from artificial sources. Several cognate subjects are also 
discussed therein, such as the number of years of ex- 
posure which pigments would require, if in the picture 
galleries of South Kensington, in order that they might 
suffer the same changes as those caused by three or 
twenty-two months' exposure in a southern aspect out- 
side the Museum. Part II. of the report contains the 
results of twelve sets of experiments with various pig- 
ments. In all the series the same paper (Whatman's) 
was used. In the paragraph relating to this subject 



372 SOUTH KENSINGTON REPORT 

there is, however, one curious error, and one obscure 
statement (p. 27). It is quite impossible that the 
paper used — its weight per ream is not given — could 
have contained so little as ' nearly i grain ' of sizing 
matter per square foot ; 10 grains is a more probable 
quantity. The sentences next following do not state 
the condition of the papers which absorbed from a moist 
atmosphere from 12*07 ^o 12-46 per cent, *of their weight 
of water.' Were they dried previously, and, if so, at 
what temperature ? We ought to have been told within 
what limits the percentage of water in these papers varied 
during the course of the trials : I have pointed out for 
many years past the importance of this hygroscopic 
moisture in paper in reference to the fading of pigments. 
Eight tints of each pigment were applied to strips of 
paper 8 inches long by 2 inches wide ; they were exposed 
in tubes open at both ends, but having the upper ex- 
tremity curved downwards so as to exclude wet and 
dirt. Of course, exposure on a wall facing nearly south 
constituted a very severe test, yet the circulation of air 
In the tubes was more advantageous to the pigments than 
would have been the steamy heat of a closed vessel, or 
even of an ordinary paper-backed picture-frame. But on 
the other hand, this arrangement allowed the free access 
to the pigments of any noxious gases, such as sulphurous 
and sulphuric acids, and sulphuretted hydrogen, which 
might have been at any time present in the atmosphere. 
The general results of this first series of trials are 
gathered in the following table, the exposure in all cases 
asting from May, 1886, until March, 1888. The pig- 
ments are arranged in the order of instability, the most 
fugitive being placed first : 



SOUTH KENSINGTON REPORT 



373 



*Carmine. 
♦Crimson lake. 
''Purple madder. 
*Scarlet lake. 
♦Payne's grey. 
♦Naples yellow. 
♦Olive green. 
♦Indigo. 

*Brown madder. 
♦Gamboge. 
* Vandyke brown. 
♦Brown pink. 
♦Indian yellow. 



Cadmium yellow. 

Leitch's blue. 
♦Violet carmine. 
*Purple carmine. 
♦Sepia. 

Aureolin. 

Rose madder. 

Permanent blue. 

Antwerp blue. 

Madder lake. 

Vermilion. 

Emerald green. 

Burnt umber. 



Yellow ochre. 
Chrome yellow. 
Lemon yellow. 
Raw sienna. 
Indian red. 
Venetian red. 
Burnt sienna. 
Terre verte. 
Chromium oxide. 
Prussian blue. 
Cobalt. 
French blue. 
Ultramarine ash. 



The pigments marked with an asterisk were found to 
have distinctly altered either in depth or hue by a much 
shorter exposure, from May to August 14, 1886. 

In a second series of trials the tinted papers were 
dried, and then introduced into the tubes, which had 
been previously heated ; the specimens were then sealed 
up hermetically ; as no moisture-absorbing material was 
enclosed with the papers, traces of water must have been 
present. My own much earlier results were abundantly 
confirmed by those obtained in this series, for the number 
of pigments which proved to be permanent under these 
conditions was double that of the first series. Brown 
madder and Prussian blue were, however, acted upon in 
this second series. Dr. Russell and Sir W. Abney make 
the remark that of the eight colours which remained 
unchanged in dry air, but were acted on in ordinary air, 
all, with the single exception of madder lake, are mineral 
colours. But this is not correct, for the pigments named 
are — madder lake, olive green, Payne's grey, sepia, Naples 
yellow, cadmium yellow, emerald green, and burnt umber, 
and of these the first four are either wholly or partly of 
organic origin, while the seventh contains an acetate. 



374 SOUTH KENSINGTON REPORT 

In the next series of experiments, the pigments were 
exposed in the presence of moisture-laden air. Very few 
colours withstood this test — none of organic origin ; both 
Prussian blue and Antwerp blue were entirely destroyed. 

An atmosphere of moist hydrogen gas was employed 
in the fourth series. Under these conditions carmine, 
crimson lake, madder lake, brown madder, olive green, 
indigo, Payne's grey, sepia, and Vandyke brown, suffered 
no change. 

When, as in the fifth series, both moisture and oxygen 
were excluded, scarcely any even of the most fugitive 
pigments were affected. Vermilion, however, as in all 
the other experiments, became black. We know that 
the reason for the change is physical, not chemical. 

In the sixth series it was proved that the addition of 
ox-gall had no beneficial effect in lessening the change of 
hue and tone in fugitive pigments. 

The remaining series, save the twelfth and last, were 
devised in order to learn what influence upon the stability 
of pigments might be exerted by admixture with Chinese 
white, by exposure to the light of the electric arc, by 
heat without light, by heat and light together, and by 
exposure to the light transmitted through coloured 
glasses. Amongst the results recorded, we may note 
the decided changes in several pigments caused by ad- 
mixture with Chinese white, and by heating the prepared 
paper slips in sealed tubes for seven hours a day for 
three weeks, all light being excluded. In a twelfth series 
of trials, the pigments were exposed in a picture-frame 
under glass in such conditions, and to such an amount of 
light, as might be taken to represent the ordinary cir- 
cumstances in which pictures are kept. The frame was 
exposed from August 6, 1886, until May 6, 1888, to very 



SOUTH KENSINGTON REPORT 375 

bright light, but not to sunshine. Gamboge, indigo, 
Naples yellow, brown pink, carmine, and Vandyke brown, 
had faded in varying degrees. Some remarks on these 
results will be found further on in the present chapter ; 
they are of extreme importance, considering the large use 
that has been made of these pigments by our water- 
coiourists, and the mild treatment to which they were 
subjected during the short period of twenty-one months. 

For the results obtained with mixtures of pigments 
under varied conditions of exposure, we must refer our 
readers to the report itself. It may, however, be re- 
marked that, in the great majority of cases, the changes 
of tone and hue which occurred were such as might have 
been predicted from the known degrees of stability of 
the several constituents of the mixtures. Here, as else- 
where in the report, we find frequent mention of the 
strange, but long known, recovery in darkness of its colour 
by Prussian blue which has been bleached by sunlight. 

In the fourth appendix to this report is an instructive 
list of the pigments employed by some of the most dis- 
tinguished artists using water-colours. Forty-six painters 
replied to the invitation of the Science and Art Depart- 
ment ; from their answers we learn that a large proportion 
of them include in their palettes many pigments which 
must be unhesitatingly condemned on account of their 
want of stability. Thus no less than seventeen out of 
the forty-six artists who responded to the appeal employ 
three of the most fugitive pigments in the series — 
namely, gamboge, brown madder, and indigo. Converted 
into percentages, we may say that 37 out of 100 
painters in water-colours use these three untrustworthy 
pigments, besides others which are worse, and others 
which are little better ; of course, they employ also 



376 



SOUTH KENSINGTON REPORT 



certain colours as to the stability of which there is no 
question. The following tabular statement gives the 
proportion of artists, per loo, who use the eleven perish- 
able pigments named below : 



Gamboge ... 


... 70 


... Faded to 7 


Indian yellow 


.. 24 


.. Faded to 6 


Vermilion ... 


.. 70 


. . Gone black 


Carmine ... 


.. 8 


.. Gone. 


Crimson lake 


.. 22 


.. Gone. 


Purple madder 


.. 28 


.. Faded to 8. 


Brown madder 


.. 74 


. . Faded to 3 


Brown pink 


.. II 


. . Faded to 7 


Vandyke brown 


•• 74 


.. Gone. 


Sepia 


.. 65 


.. Faded to 8. 


Indigo 


•• 52 


. . Faded to 8. 



I represents the 
lightest tint, 8 the 
darkest. The washes 
of pigment were fully 
exposed for twenty- 
two months. 



We call these pigments perishable with good reason. 
For, according to the report under review, all of them were 
found to have faded, materially and conspicuously, after 
twenty-two months' full exposure in a south aspect, while 
three of them had entirely disappeared, and another (ver- 
milion) had become black. But this is not all. For under 
a less severe trial (p. 45) — namely, exposure for the 
same time, not to direct sunlight, but to a very bright 
light from a window, ' under conditions approximating to 
those to which pictures are usually subjected ' — six out 
of the eleven pigments had faded, though in varying 
degrees. With these figures and results before us, it is 
impossible to resist the conclusion that a life of 100 years 
is too much to allow to many of the water-colour drawings 
of the present day. What shall we say, then, as to the 
stability of the works of the earlier masters of the English 
water-colour school ? How much care in the exclusion 
of ' the more fugitive colours * was taken by the water- 
colourists of 1780 to 1850 ? Could it be honestly said of 
any large number of such works, in which gamboge 



TRIALS OF WATER-COLOUR PAINTS 377 

brown pink, crimson lake, sap-green, indigo, and sepia, 
were generally employed without stint, ' that about a 
century of exposure v/ould have to be given to water- 
colour drawings in galleries lighted as are those at South 
Kensington before any marked deterioration would be 
visible in them '? * (Report, p. 46.) 

Dr. Russell and Sir William Abney add, indeed, the 
proviso, ' If painted with any but the more fugitive 
colours.' But this condition cannot be said to have been 
fulfilled by the works in question ; for in the great 
majority of them, most of the six fugitive pigments which 
we have just named were freely employed. And it is 
these very pigments which have been proved by the 
reporters themselves to suffer ' marked deterioration ' by 
an exposure of twenty-one months only to strong daylight 
without direct sunshine. Moreover, it must not be for- 
gotten that the fading of a single important pigment in a 
water-colour drawing is ruinous to the whole effect, de- 
stroying the balance of the chromatic scheme of the artist 
more effectually than a slight, but equal, degradation of 
all the hues. 

An instructive set of trials of water-colour paints was 
commenced in May, 1894, ^.nd continued for four years 

* In the preceding brief resume of certain parts of the South 
Kensington Report no reference has been made to an argument, 
developed in §§ x. to xv., in which it is contended that ' if a certain 
tint be exposed to an intensity of radiation which we will call 100, 
and which bleaches it in, say, i hour, then, if a similar tint be 
exposed to an intensity i, it will require 100 hours' exposure to it 
to effect the same bleaching.' The universal applicability of this 
conclusion cannot be conceded by those who are familiar with 
numerous instances in which no chemical or physical change 
occurs when certain substances are exposed continuously for long 
periods to a particular temperature, yet, when they are heated but 
a degree or two higher, instantly alter, decompose, or react, as the 
case may be. 



378 



TRIALS OF WATER-COLOUR PAINTS 



by a sub-committee of the Burlington Fine Arts Club. 
The results of these experiments have been embodied in 
three reports. Winsor and Newton's moist water-colours 
were used, flat washes on Whatman's * not hot pressed ' 
paper of the year 1888 being exposed to light in the 
windows of the billiard-room of the club. One of the sets 
so exposed was in an ordinary glazed frame, another set 
was enclosed in hermetically sealed glass tubes containing 
ordinary air ; while a third set was contained in similar 
tubes, but the atmosphere present was maintained in a 
dry state by means of a reservoir of burnt lime which 
absorbed all or almost all traces of water in the pigments, 
the paper, and the mount. The final comparisons were 
made with parallel sets which had been kept in absolute 
darkness. We give here, in tabular form, the condition 
of the paints at the end of the fourth year of exposure : 
reference must be made to the original reports for infor- 
mation as to the results of six months' and of thirteen 
months' exposure to sunshine. 



RESULTS OF EXPOSURE FOR FOUR YEARS, 
MAY 25, 1894, TO MAY 25, 1898 



FROM 



Pigment 

Aureolin 
Gamboge 
Indian yellow 
Cadmium yellow 
Vermilion 
Crimson lake ... 
Rose madder ... 

Indian red 
Madder carmine 



(Original depth = 10) 



Set in Dry 
Air 
No change. 
Faded to i. 
Gone. 

Deeper orange. 
Greyish. 
Faded to 0*5. 
Faded to 8-5. 

No change. 
Faded to 9. 



Set in Moist 

Air 
Faded to 9. 
Faded to i. 
Faded to i. 
No change. 
Greyish. 
Gone. 
Faded to 8*o 

and purplish. 
No change. 
Darker, more 

purplish. 



Set in Frame 

No change. 

Faded to i. 

Faded to i. 

No change. 

Greyish. 

Gone. 

Faded to 85 

and purplish. 
No change. 
Darker, more 

purplish. 



TRIALS OF WATER-COLOUR PAINTS 



379 



Pigment 


Set in Dry 
Air 


Set in Moist 
Air 


Set in Frame 


Madder brown 


Faded to 9. 


Faded to 6, 


Faded to 8, 






purple gone. 


purple gone. 


Madder purple 


Faded to 8. 


Faded to 4. 


Faded to 5. 


Prussian blue ... 


No change. 


Faded to i. 


Faded to 85. 


French blue 


No change. 


No change. 


No change. 


Indigo 


No change. 


Faded to i, 


Faded to i 






greenish grey. 


greenish grey. 


Vandyke brown 


Faded to 2, less 
yellow. 


Faded to i. 


Faded to i. 


Sepia 


Faded to 8. 


Faded to i . 


Faded to 4. 


Indigo with In- 








dian red 


No change. 


Indigo gone. 


Indigo gone. 



The most striking results of these trials was the com- 
plete stability of Prussian Blue and of Indigo when exposed 
in air kept dry. The further remark may be made that 
moist air, that is, ordinary air containing moisture and 
confined in a sealed tube, inflicts more injury upon 
alterable pigments than ordinary air enclosed in a frame 
which does admit of some amount of ventilation occurring. 
There is no difficulty in so constructing a frame as to 
introduce a water-absorbing substance which may be 
renewed from time to time. Thus we shall be able to 
employ with confidence in water-colour painting madder 
brown, madder purple, Prussian blue, indigo and sepia — 
five pigments which under ordinary conditions of ex- 
posure to sunshine suffer serious changes. But no method 
has yet been devised by means of which we may safely 
use gamboge, Indian yellow, vermilion, crimson lake and 
Vandyke brown, although it must be stated that instances 
have been recorded in which vermiUon as a water-colour 
has stood very severe exposure-tests, especially when 
white of egg has been mixed with it. 

Amongst the series of trials of oil-paints made by the 
author of this handbook, one set first arranged in 1880 



38o EXPERIMENTS WITH OIL-PAINTS 

may be described here. Chance's colourless plate-glass 
was employed as the painting-ground, so as to avoid all 
interference with the pigments from the surface on which 
they were spread ; glass presents the further advantage 
of permitting a complete examination of the back of each 
specimen, and of changes in its translucency, opacity, or 
texture. Each glass measured 8 inches by 6 ; the com- 
plete series was prepared in duplicate — one for preserva- 
tion in darkness, the other for exposure to all the light 
that could be secured (in Kew) during live years in a 
window facing nearly south-west. The majority of the 
paints tried were obtained from four firms (Messrs. Winsor 
and Newton, Messrs. Roberson and Co., M. Edouard of 
Paris, and Schoenfeld of Diisseldorf). Specimens of 
each pigment were reserved for further examination and 
analysis. Some of the chief results obtained are given 
in the annexed table; a few remarks on the changes 
observed in some of the pigments which had been mixed 
with flake white are added : 



Pi<yment "^^^^'^ ^^ 


Residual Depth Change of Hue 


figment Exposure 


[Original- 


: 10) and Remarks 


Yellow ochre 


5 


10 ., 


.. Browner; more translu- 
cent. 


Aureolin 


5 


9 •• 


. None. 


Indian yellow 


5 


8 .. 


. Slighdy brownish. 


Naples yellow (true) 


5 


10 .. 


. None. 


Pale yellow madder 


2 


7 .. 


. Greyish salmon when 
mixed with flake white. 


Deep yellow madder 


2 


6 .. 


. Dirty pink when mixed 
with flake white. 


Laque brun jaune ... 


2 


7 .. 


. Lost much yellow. 


Laque brun fonce ... 


2 


8 .. 


. Lost much yellow. 


Laque Robert, No. 5 


2 


2 .. 


. Warm grey when mixed 
with flake white. 


Laque Robert, No. 6 


2 


4 .. 


. Warm grey when mixed 
with flake white. 


Scarlet lake 


5 


7 •• 


. Dull pinkish red. 



TRIALS OF OIL-PAINTS 



381 



Years of 
Exposure 

5 
2 



Residual Depth 
{Original =10) 



I 
10 

9-5 

9 

8-5 

8 
10 



Change of Hue 
and Remarks 

Almost gone. 

None. 

None. 

Rather duller. 

Slightly greener. 

Slightly greener. 

None. 



Pigment 

Crimson lake 
Madder red ... 

Madder carmine ... 5 

Madder brown ... 2 

Prussian blue ... 5 

Indigo 5 

Artificial ultramarine 5 

A series of trials of seventeen madder colours in oil 
was carried out in 1893. These were all prepared by 
Lefranc of Paris. The samples were spread on thin 
lantern glass 4 in. x 4 in., and when dry each glass was 
cut in half. One half was exposed to sunshine from 
March 26 until October 26, the other half of each specimen 
being kept in darkness. At the end of the seven months 
the halves of each sample were rejoined and carefully 
mounted, and thus an instructive set of slides obtained. 
The results are given in the following table, in which I 
have grouped together those varieties of 'laque de garance' 
which resembled one another in their degree of stability : 

Name _ 
Laque de garance fonce 

, , , , rose intense 

,, ,, brun rouge 

,, ,, rouge brun 
Laque de garance rose 

, , , , rose dore 

brun pourpre ... 
Laque de garance pourpre 

,, ,, pourpre concentre 

Carmin de garance ... 
Laque de garance brun de madder 

,, ,, brun 

,, ,, brun fonce 

,, ,, jaune capucine 

,, ,, brun jaune 

,, ,, nuance bitume 



-Little or no change. 



Slight change. 



-1 



Marked change. 



Lost from 40 to 80 per 
cent, of their original 
depth. 



382 TRIALS OF OIL-PAINTS 

In the fourth or least stable group, comprising the 
varieties of madder brown, it was noticeable that the 
yellow constituent of the colour was most affected by 
exposure, the bmn fonce and the nuance hitume losing all 
their characteristic beauty of hue and becoming of a dull, 
poor, rusty tint and not retaining over 20 per cent, of 
their original depth. Even in Group II. the golden hue 
of the rose doree was the only chromatic element of this 
madder paint which had been lost to an appreciable 
extent during the six months' exposure. 

Experiments as to the degree of stability possessed by 
many other oil-paints have been made ; the results will 
be found for the most part incorporated with the accounts 
given of the several pigments in Part III. One remark 
may perhaps be usefully introduced in this place with 
reference to the differences observable in the quality and 
behaviour of pigments bearing the same name but ob- 
tained from different artists' colourmen. It is a good 
plan to place side by side on three trial-plates several 
* makes ' of the same paint and to keep one set in dark- 
ness, and to expose a second set to sunshine and a third 
set to strong diffused daylight. It will sometimes be 
found that the fascinating colour-quality v/hich at the 
first glance recommends one sample is not preserved 
after exposure, although the reverse experience is not 
uncommon. It must not be forgotten that although the 
composition and constituents of the vast majority of pig- 
ments, both natural and artificial, are known, yet there 
are differences in the methods of preparation which, in 
some cases at least, are kept secret, and which result not 
in differences of nuance only, but in differences of stability 
also. 



INDEX 



Abney, Sir W,, 348, 371 
Acetic acid, 85, 224 
Acetone, 109 
Actinic rays, 56, 348 
Adjective pigments, 281 
Albumen, 85 
Alcohol, no 
Alizarin, 194, 196 

„ crimson, 194 

„ lakes, 196 

„ orang-e, 185 

„ yellow, 1 85 
Alterable pigments, 283 et seg. 
Alum in paper, 12, 14 
Alumina, hydrate, 50 
. „ linoleate, 67, 190 

„ oleate, 67, 190 
Aluminium, sheet, 39, 41 
Amber, 69 

„ oil of, 71 

„ varnish, 135 
Amyl acetate, 355 
„ alcohol, 112 
Andrew, F. W., the late, 362 
Anime, 73 
Anti-vermilion, 189 
Arabic acid, 92 
Arnold paper, 9 
Arrabida red, 204 
Arsenic sulphides, 184 
Asbestos, 26 

„ in plaster, 22 
Asphaltum, 260 
Aureolin, 168 
Aurora yellow, 166 
Azurite, 249 

Back, the, of pictures, 31, 38, 345 
Balsams, 78 



Barium chromate, 171 

,, hydroxide, 104 

,, sulphate, 148 
Baryta- water, 104 

„ white, 148 

„ yellow, 171 
Bassorin, 94 
Beeswax, 79 
Bell's medium, 140 
Benzene, iii 
Bistre, 259 
Bitumen, 260 
Black, ivory, 270 

„ lead, 270 

„ pigments, 264 
Bleaching oil, 56 
Bleu lumiere, 249 
Blockz, J., 361 
Blue, Antwerp, 240 

„ black, 269 

„ cobalt, 234 

„ Egyptian, 250 

„ indigo, 241 

,, pigments, 226-251 

,, Prussian, 236 

„ Turnbull's, 238 

,, verditer, 249 
Brown, Caledonian, 256 
„ Cappagh, 259 
,, pigments, 252-263 
,, pink, 181 
„ Vandyke, 257 
Burlington Club trials, 378 
Burnt carmine, 209 

„ lime, 19 

,, sienna, 256 

,, umber, 254 
Burton's cobalt, 235 

,, potters' pink, 200 



383 



384 



INDEX 



Cadmium, green, 225 

„ pale, 162 

„ red, 166 

,, versus chrome, 183 

,, yellow, 162 
Calcium carbonate, 19, 23 

,, hydroxide, 19 

„ oxide, 19 

,, silicate, 20, 304 

„ sulphate, 23, 27, 307, 35^ 
Caledonian brown, 256 
Camphor, 119 
Canada balsam, 79 
Canvas, 34 

,, back of, 37 

,, preservation of, 36-39 

,, priming of, 34 

,, Willesden, 41 
Cappagh brown, 258 
Carbon bisulphide, 108 
Carbonate of copper, 221, 249 
„ lead, 145 
lime, 19 
Carbonates, 277, 279 
Carmine, 207 
Cassel brown, 25S 
Cellulose, 11 

Ceramic pigments, 200, 218, 235 
Ceresin, 81 

Cerulean blue or cerulium, 235 
Chafing varnish, 353 
Charcoal blacky 268 
Chessylite, 249 
Chinese ink, 265 

„ vermilion, 189 
„ white, 152 
Chloroform, 109 
Chromates, 279 
Chrome green, 214, 216 

„ yellow, 182 
Chromium, green oxide of, 214 
Cineol, 107, 123 
Cinnabar, 187 
Citral, 123 

Coagulation of albumen, 85 
Cobalt blue, 234 

„ „ Burton's, 235 

„ green, 218 

„ resinate, 57 

„ violet, 211 

,, yellow, 1 68 
Cobaltinitrites, 168 
Coccus cacti, 207 

„ ilicis, 207 



Coccus lacca, 205 

Cochineal lake, 207 

CcEruleum, 235 

Collodion, 37 

Conservation of pictures, 38^/ seq., 342 

Copal, Angola, 73 

„ Benguela, 73 

,, Kauri, 74 

„ oil of, 139 

„ oil-varnish, 135 

,, pebble, 72 

,, Sierra Leone, 72 

,, spirit varnish, 133 

,, West Indian, 74 

,, Zanzibar, 73 
Copals compared, jj 
Cotton paper, 11 
Cowdi resin, 74, 138 
Cremnitz white, 148 
Crimson lake, 208 
Cyanine, 240 
Cymene, 124 
Cyprusite, 161 

Dammar, 74 
Dextrin, 97 
Dextrose, 97 
Diluents, 106-124 
Dipentene, 118 
Distilled water, 106 
Dryers, 55, 57, 125 

Egg-medium, 85 

Egyptian blue, 250 

Elements, 275, 276, 278 

Elemi, 142 

Emerald green, 219 

Emerald oxide of chromium, 216 

Emulsions, 87 

Epichlorhydrin, 11 1 

Esparto, 12 

Ether, 108 

Ethereal hydrogen peroxide, 17, 151 

Eucalyptol, 123 

Eucalyptus oils, 122 

Ferrocyanides, 236 
Flake white, 145-15 1, 328 

„ action on oil, 64, 32S 

Freeman's white, 151 
Fresco grounds, 21, 22. 

,, method, 303 

,, secco, 22, 305 
Frescoes, Asiatic, 28, 307 



INDEX 



385 



Frescoes, protected and restored, 356 
Fugitive pigments, 2S4, 287, 2S9 

Galleries, picture, 38, 342, 349 

Gambier Parry's medium, 142, 315 

Gamboge, 172 

Gelatin, 10, 88 

Geraniol. 107 

Gesso, 32 

Glass, protective, 348 

Glue, 35. 88 

Glycerides, 51 

Glycerin, 51, 98 

Gold-point, 322 

Graphite, 270 

Green, chrome, 214 

,, madder, 285 

„ oxide of chromium, 214 

„ ultramarine, 232 

,, verditer, 221 
Gum arable, 91 

„ British, 97 

„ Cape, 94 

„ Senegal, 92 

„ Suakim, 92 

„ tragacanth, 93 
Gypsum, 22, 23, 27 

Hartley, the late Sir W. N., 366 

Hellige's colorimeter, 363 

Hodgkinson paper, 9 

Honey, 97 

Hydrate of alumina, 50, 194, 208 

Hydrates of copper, 249 

„ iron, 157, 202 

Hydrocarbons, 81, in, 11 2-1 17 
Hydrogen peroxide, 35, 151 
Hydroxides or hydrates, 279 

Illuminated manuscripts, 190, 331 
Indian ink, 264 

„ lake, 205 

,, red, 202 

,, yellow, 174 
Indigo, 241 

„ brominated, 247 

„ synthetic, 247 
Infusorial earth, 16 
Ink, Indian, 264 
Intonaco, 21 
Iron, compounds of, 157, 177, 200- 

205 
Ivory, 19 

„ black, 270 



Kauri, 74, 138 
Kermes lake, 207 
Kieselguhr, 16 
Kings' yellow, 184 
Kowdi, 74, 138 

Lsevulose, 97 

Lamp-black, 267 

Lapis lazuli, 226 

Laurie, Prof. A, P., viii, 22, 250, 313 

Lavender, oil of, 122 

Lead antimoniate, 178 

,, chromate, 182 

„ dryers, 55, 59 

,, oxychloride, 152 

,, ■ red, 210 

„ sugar of, 125 

„ sulphate, 151 

„ white, 145-15 1 
Lecithin in egg-yolk, 87 
Leitch's blue, 240 
Lefranc's madders, 381 
Lemon, oil of, 123 

„ yellow, 171 
Light, action of, 56, 342-349, 358-382 

,, red, 200 
Lime, burnt, 19, 20 

„ carbonate, 18 

„ caustic, 19, 22 

„ hydrate, 19 

,, mild, 19 

„ -putty, 20 

,, slaked, 19 

„ sulphate, 23, 27 

,, -water, 19, 102 
Limonene, 118, 123 
Linen fibre, 7, 11 
Linoleic acid and linolein, 51 
Linoleum, 40 
Linoxine, 51 
Linseed, 47 
Linseed oil, 47-51 

„ „ siccative, 57 
,, „ testing, 60 
,, white, 48 
Litmus, 13 
Lovibond's tintometer, 359 

Madder brown, 196, 198 

„ lakes, 194 

„ rose, 198 
Malachite, 221 
Manganese borate, 57 
„ dryers, sj 

25 



386 



INDEX 



Manganese oil, 58 


Oils,d 


rying, 46 


„ resinate, 57 


„ fixed, 45 


„ violet, 251 


Old paintings, 325-341 


Manuscripts, illuminated, 190, 331 


Orang 


e, oil of, 123 


Marouflage, 26 


Organic pigments, 277, 2S0 


Mars violet, 177, 203 


Orpiment, 184 


„ yellow, 177 


Ossein 


, 16 


Mastic, 76 


Ostwald, Dr. W., notes by, 37-40, 52- 


„ varnish, 131 


^55> 


J 1 9-32 1 


Mediums, 139-142 


0. W 


paper, 9 


Megilp, 140 


Oxides, 276, 278 


Mercury lamp, 56 






Methylated spirit, 109 


Pamters' materials, i 


Mineral lake, 199 


Painting methods, 301 


,, pink, 200 


,, 


,, Central Asian, 28, 


„ violet, 251 




307 


Mixed varnishes, 130 


,, 


„ distemper, 22, 301 


Mummy, 262 


,, 


,, fresco, 21, 304 




>> 


„ Gambler Parry, 25, 


Naphthalene as resin-solvent, 13S 




309 


Naples yellow, 178 


,, 


oil, 309 


National Gallery, 331 




pastel, 318-321 


„ British Art, 335 


j> 


,, stereochromy, 24, 


„ „ Portrait, 336 




307 


Newman's colours, 370 


„ 


,, tempera, 22, 301 


Nut-oil, 62 


" 


water-colour, 317, 
362 


Ochre, chrome in, 161 


» 


, , water-glass, 24, 307 


„ Perigord, 159 


Panels 


,29 


,, red, 204 


}) 


preparation of, 30 


,, yellow, 157 


Paper, 


7 .,. 


Oil, action on paints, 63 


>) 


acid in, 13, 369 


,, amber, 119 


>■> 


alum in, 10, 13, 14 


„ copal, 119 


>> 


analyses of, 9 


„ drying, 46 


,, 


ash of, 10 


,, eucalyptus, 122 


,, 


cotton, II 


,, extraction, 47 


5> 


fibre in, 1 1 


,, in egg-yolk, 87 


,, 


linen, 9, 1 1 


,, m paints, 65 


„ 


size in, 10, 14 


,, lavender, 122 


,, 


sugar, 17 


,, lemon, 123 


,, 


testing, 12 


,, linseed, 47-51 


,, 


Turner, 17 


„ manganese, 58 


,, 


Varley, 17 


„ nut, 62 


,, 


water in, 9 


„ orange, 123 


,, 


wood-pulp in, 12, 17 


,, painting, 309 


Paraffi 


n, 81, 120 


,, poppy, 61 


>> 


copal medium, 141 


„ rosemary, 123 


,, 


on frescoes, 357 


„ semi-drying, 46 


>•> 


paste, 356 


,, siccative, 46, 57 


Parchment, 16 


,, turpentine, 112 


Pastel painting, 318-321 


,, tung, 63 


Payne- 


s grey, 273 


,, varnishes, 135 


Perigord, orange and raw, 159 


Oils, essential, 122 


Permanent pigments, 284-288 



INDEX 



387 



Peroxide of hydrogen, 150, 338 
Petroleum spirit, 120 
Phellandrene, 117 
Pigments classified, 274 

,, interacting, 275 
Pinene, X17 
Piuri, 174 
Plaster, 18-28 
Platinum-point, 322 
Poppy oil, 6 1 
Potters' pink, 200 
Primrose yellow, 172 
Prussian blue, 236 

,, brown, 263 
Punicin, 247 

Purple, Tyrian, 247, 334 
Purpurin, 194 

Queen's House, Greenwich, 358 

Raw sienna, 254 

„ umber, 253 
Red lead, 210 
,, ochre, 204 
,, pigments, 186-21 1 
Resin, 68 

„ amber, 69 

„ anime, 73, 74 

„ copal, 72-77 

„ cowdi, 74 

,, dammar, -js 

,, kauri, 74 

,, mastic, 76 

,, sandarac, 75 
Resinates, 55, 59, 69, 113 
Restoration of pictures, 351 
Restricted palettes, 294-298 
Reynolds, Sir Joshua, 292, 338, 361 
Roberson's medium, 140 
Rock crystal to be avoided, 349 
Rood, Prof. O. N., 365 
Rose madder, 198 
Rosemary, oil of, 123 
Rosin, 113 

Rosinates, 55, 59, 113 
Royal Exchange panels, 26 
Ruskin, John, 347 
Russell, Dr. W. J., the late, 371, 373 

Sandarac, 75 

„ varnish, 76 
Scheele's green, 221 
Schweinfurt green, 219 
Selected palettes, 290 



Sepia, 272 

Siccatives, 55, 125-129 

Sienna, burnt, 256 
„ raw, 254 

Silicates, 277, 279 

„ alkaline, 100, 307 

Silver-point method, 321 

Simpson, W., the late, 369 

Size, 35, 88 

Size-painting, 303, 332 

Slate, 27 

Slate-grey, 273 

Smalt, 248 

Soane Museum, 151, 338 

Solvents, 106-124 

South Kensington Museum, 338, 348 
y> „ Report, 371 

Spike, oil of, 122 

Spirit-fresco grounds, 25 
„ medium, 142 

„ method, 142, 315 

Starch, 94 

„ soluble, 95 

Stein, Sir Aurel, 8, 28, 307 

Stereochromy, 24, loi, 307 

Stone, 18, 27 

Strasburg turpentine, 78 

Straw in paper, 12 

Substantive pigments, 281 

Sugar-paper, 17 

Sulphides, 276, 278 

Sylvestrene, 118 

Taylor, Mr. J. Scott, viii, 218 
Tempera-grounds, 22 
„ method, 301 
Terpenes, 112-123 
Terre verte, 212 

„ „ adulterated, 214 
Testing paper, 12 
„ pigments, xi 
„ turpentine, 115 
Toluene, 111 
Turnbull's blue, 238 
Turner paper, 17 
Turpentine, 112 

„ oil of, 116 

„ Strasburg, 78 

„ Venice, 78 

Turpentines, 112 

Ultramarine, 226 

„ artificial, 229 

ash, 227 



388 INDEX 

Ultramarine, ffreen, 232 

„ lilac, 232 

„ red, 232 

„ testing, 233 

„ violet 232 

Ultra-violet rays, 56, 318 
Umber, 252 



Vanadium yellow, 183 
Varley paper, 1 7 
Varnish, amber, 133, 135 

„ copal, 133-140 

„ mastic, 131 
oil, 131, 135 

,, sandarac, 133 

„ spirit, 131, 133 
Varnishes, 130-139 
Vellum, 16 
Venetian red, 201 
Venice turpentine, 78 
Verdig-ris, 223 
Verditer, 221, 249 
Vermilion, artificial, 187 

„ instability of, 190 

„ native, 186 

„ tested, 189 

Vernalis, 218 
Victoria and Albert Museum, 338, 

348 
Vine black, 269 
Violet, cobalt, 211 

„ manganese, 251 

,, ultramarine, 232 
Viridian, 216 
Viscose, 14 

Wallace Collection, 337 
Ward, Mr. James, 357 
Water, 106 

„ baryta-, 18, 104, 304 



Water in drawings, 345 

„ in paper, 9, 317 

„ in resms, 69 

„ lime-, 19, 102, 304 
Water-colour method, 317 
Water-glass, 100 
Wax, bees', 79 

„ Brazilian, 80 

„ Ceresin, 81 

„ Chinese, 80 

,, Japanese, 81 

,, -painting, 80 

„ paraffin, 81 
Whatman paper, 9, 12, 371, 378 
White-lead, 145 

„ „ action on oil, 64 

„ „ adulteration of, 147 

„ ,, bleaching discoloured, 150 

„ „ defects of, 149 

„ „ impurities in, 147 
White of egg, 85 
White pigments, 145-156 
Willesden canvas, 41 
Wood, 29-33 

„ pulp, mechanical, 17 

„ spirit, 109 

Yellow, cobalt, 168 
„ kings', 184 
„ lake, 180 
„ madder, 181, 185 
„ ochre, 157 
„ pigments, 157-185 



Zinc borate, 128 
„ chromate, 172 
„ oxide, 152 
„ sulphate, 129 
„ sulphide, 154 
„ white, 152 



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pp. xii + 56. 40 copies only. {Privately Printed, i8gg. 

RECORDS AND RECOLLECTIONS. 9 Illustrations. 
Part II., with Index. Pp. x -^50. 40 copies only. 

[Privately Printed, 1909. 

JAPANESE SWORD GUARDS. 273 Collotype Illustrations 
of Specimens from the Author's Collection. Pp. x + 8o. 100 
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